Health coverage would be expanded under the Democrats’ spending plan.

President Biden pleaded with House Democrats on Thursday to embrace his “framework” for a $1.85 trillion economic and environmental bill, saying its fate would help determine that of his presidency and his party’s hold on Congress, and its success would restore the nation’s standing on the world stage.

But the president’s appeal appeared to have failed to break the logjam among Democrats. Crucial details of the legislation remained in flux, and progressives declared they would not bow to pressure to quickly throw their support behind a separate $1 trillion bipartisan infrastructure package that has already passed the Senate.

By Thursday night, House leaders had scrapped plans for a vote on the public works measure, and the chamber approved a short-term extension of transportation programs through early December, a sign that passage of both the infrastructure bill and the domestic policy plan may be far off.

It was a setback after an audacious gamble by Mr. Biden, who had delayed his departure for a trip to Europe to try to nail down an accord on his domestic agenda. He used a morning meeting at the Capitol to attempt to rally House Democrats around the emerging deal.

“We have a framework that will get 50 votes in the United States Senate,” Mr. Biden told the group, according to a person familiar with his private remarks. “I don’t think it’s hyperbole to say that the House and Senate majorities and my presidency will be determined by what happens in the next week.”

Later, in public remarks at the White House, Mr. Biden hailed the plan as “historic.”

“No one got everything they wanted, including me,” he said in the East Room before departing on a trip to Rome. “But that’s what compromise is. That’s consensus. And that’s what I ran on.”

House leaders hoped the framework would be enough to persuade the chamber’s most liberal members that Congress was on the verge of passing a truly progressive package — and that those liberals, in turn, would join more moderate and conservative Democrats to send the infrastructure bill to the president for his signature.

“We badly need a vote on both of these measures,” Mr. Biden privately told lawmakers on Thursday morning, according to the person familiar with his remarks.

But liberals were still unsatisfied with a plan that was clearly unfinished — and that omitted many of their cherished priorities.

“What I would say is you have the outline of a very significant piece of legislation — I want us to make it better,” said Senator Bernie Sanders, the Vermont independent and Budget Committee chairman.

The change of course on holding an infrastructure vote on Thursday was a sign that the last-minute visit by Mr. Biden had not been enough to assuage progressives worried about the fate of the economic and environmental bill.

“Members of our caucus will not vote for the infrastructure bill without the Build Back Better Act,” Representative Pramila Jayapal, Democrat of Washington and the chairwoman of the Congressional Progressive Caucus, said in a statement that endorsed the president’s outline. “We will work immediately to finalize and pass both pieces of legislation through the House together.”

Two crucial holdouts, Senators Joe Manchin III of West Virginia and Kyrsten Sinema of Arizona, had yet to publicly commit to voting for the social policy legislation.

In a statement, Ms. Sinema stopped substantially short of such a promise, although she sounded an upbeat note on the talks.

“After months of productive, good-faith negotiations with President Biden and the White House, we have made significant progress on the proposed budget reconciliation package,” she said.

Mr. Manchin did not commit to supporting it either, saying, “It’s in the hands of the House.”

But one person close to both senators said they had privately indicated that they supported Mr. Biden’s framework.

The package is considerably more modest than the cradle-to-grave expansion of the safety net that Mr. Biden initially envisioned, having been stripped of ambitious climate change programs and provisions to provide federal paid leave, a broad expansion of Medicare and two years of free community college.

But provisions to provide universal preschool for more than six million 3- and 4-year-olds and subsidies to limit the costs of child care to no more than 7 percent of income for most families would offer a significant boost to the middle class.

And about $555 billion for programs to move Americans to electric vehicles and entice utilities away from natural gas and coal would be the largest federal investment in combating climate change.

Democratic leaders had been keen to hand Mr. Biden a victory before he arrived overseas for a week of summitry. The president is scheduled to attend a climate summit on Monday in Scotland, where he hoped to point to the deal as evidence of the United States’ commitment to tackling climate change.

President Biden rolled out his $1.85 trillion framework for an environment and social policy plan with great fanfare on Thursday, pitching it as a package that could unite his fractious party. But in reality, the proposal was more of an outline of a bill whose major components and key details were still being hammered out.

Even after directing members to an early version of the plan’s legislative text, Speaker Nancy Pelosi of California suggested there were additional changes to come, including her desire to add back a proposed federal paid family and medical leave program that Mr. Biden omitted.

White House officials and top Democrats also continued to negotiate over a costly tax provision, a plan to lower the cost of prescription drugs, and a proposal to allow the Internal Revenue Service access to bank account information to help crack down on tax cheats, among other components that could have a large impact on the size and shape of the plan.

For instance, a fact sheet released by the White House omitted a provision that is a top priority of lawmakers from New York, New Jersey and other high-tax jurisdictions that would lift the cap on how much in state and local taxes people can deduct from their federal taxes. Lawmakers from those states have warned that they could not support the bill without its inclusion.

Representative Richard E. Neal of Massachusetts, the chairman of the tax-writing Ways and Means Committee, said that it was likely that the final measure would, in fact, include the so-called SALT provision, which is likely to cost hundreds of billions of dollars and would amount to a large tax cut for upper-middle-class people.

Mr. Biden’s outline also did not include the bank reporting provision, after Senator Joe Manchin III of West Virginia, a crucial swing vote, expressed concerns about it, but an administration official said the White House was still working with him to win his approval for adding it to package. Negotiators were optimistic about reaching a deal on the measure, which is estimated to generate substantial sums to pay for the broader legislation.

And an intensive set of talks continued on prescription drug pricing after Senator Kyrsten Sinema of Arizona and centrists in the House effectively rejected a proposal to allow Medicare to negotiate the price of medications. A narrower provision Ms. Sinema had been discussing with White House officials — which would have limited drug price negotiations to a small subset of outpatient medications like chemotherapy drugs that had passed their period of patent exclusivity — was left out of Mr. Biden’s announcement on Thursday.

But Democrats were toiling to restore it.

“The prescription drug deal on the table isn’t everything I want, but it’s not a fig leaf,” Senator Chris Murphy, Democrat of Connecticut, wrote on Twitter. “It’s likely $100B in cuts to drug company profits with the money to be used to cut out of pocket costs for seniors in half.”

Senator Bernie Sanders, the Vermont independent and Budget Committee chairman, also vowed to keep pressing for a broader expansion of Medicare, after his initial proposal to add hearing, vision and dental benefits was cut back to only cover hearing.

President Biden met with lawmakers on Thursday morning to lay out a framework on a $1.85 trillion effort to spend heavily on climate change, child care and a wide range of other economic programs, paid for by an estimated $2 trillion in tax increases on corporations and high earners, though it was not immediately clear if it has the votes to pass.

White House officials refused to say if all holdout Democrats in Congress had expressed support for the framework, which still may change.

The framework leaves out several key planks of the economic agenda that Mr. Biden laid out on the campaign trail and shortly after taking office. It does nothing to reduce prescription drug costs for seniors, and it omits what would have been the nation’s first federally guaranteed paid family and medical leave for workers. It does not include free community college for all, as Mr. Biden had promised. It would expand Medicare coverage to include hearing, but not vision or dental services.

It also would not raise the corporate tax rate or the top individual income tax rate, and it would not impose a new tax on the unrealized wealth gains of billionaires, as Democrats had recently proposed.

The key provisions of the proposal include:

• $555 billion to fight climate change, largely through tax incentives for low-emission sources of energy.

• $400 billion to provide universal prekindergarten to 3- and 4-year-olds, and to significantly reduce child care costs for working families earning up to $300,000 a year.

• $200 billion to extend an expanded tax credit for parents through 2022, and to permanently allow parents to benefit from the child tax credit even if they do not earn enough money to have income tax liability.

• $165 billion to reduce health care premiums for people who are covered through the Affordable Care Act, to provide insurance for an additional four million people through Medicaid and to offer hearing coverage through Medicare.

• $150 billion to reduce a waiting list for in-home care for seniors and disabled Americans, and to improve wages for home health care workers.

• $150 billion to build one million affordable housing units.

• $100 billion for immigration streamlining, in part to reduce a backlog of nine million visas. House Democrats proposed provisions last month to address the legal immigration system, including a plan to recapture hundreds of thousands of unused visas various administrations failed to use over several decades and allow green card applicants to pay higher fees to expedite their processing. The investment outlined on Thursday would also expand legal representation for migrants and streamline processing at the southwest border, officials said. Mr. Biden has faced criticism from both Republicans and Democrats for his handling of migration to the border.

• $40 billion for worker training and higher education, including increasing annual Pell grants by $550.

Offsetting that spending is an estimated $2 trillion in revenue increases, including:

• A 15 percent minimum tax on the reported profits of large corporations.

• Efforts to reduce profit-shifting by multinational companies, including a separate 15 percent minimum tax on profits earned by U.S. companies abroad — and tax penalties for companies that have their headquarters in global tax havens.

• A 1 percent tax on corporate stock buybacks.

• Increased enforcement for large corporations and the wealthy at the Internal Revenue Service.

• An additional 5 percent tax on incomes exceeding $10 million a year and another 3 percent tax on incomes above $25 million.

• Efforts to limit business losses for the very wealthy and to impose a 3.8 percent Medicare tax on certain people earning more than $400,000 a year who did not previously pay that tax.

President Biden’s urgent appeal for a fast House vote on the $1 trillion infrastructure bill on Thursday was quickly rejected by the House’s liberal wing, which continued to demand more tangible progress on its priority — the larger social policy and climate change bill.

Mr. Biden made the case for both his outline for a $1.85 trillion economic and environmental bill and an immediate House vote on the infrastructure bill in a morning meeting at the Capitol. By early afternoon, it was clear that too many progressive House members were not won over by the promise of a “framework” alone. Representative Cori Bush, Democrat of Missouri, said she felt “a little bamboozled.” Representative Rashida Tlaib, Democrat of Michigan, said she was a “hell no.”

Representative Ilhan Omar of Minnesota, the Congressional Progressive Caucus’s vote counter, emerged from a closed-door caucus meeting to say House Democratic leaders still lacked the votes to pass the infrastructure bill, despite Mr. Biden’s appeal for a legislative victory to bring to Europe this weekend.

By Thursday evening, House leaders had decided against going ahead with an immediate vote on the infrastructure measure, pushing off its consideration until at least next week.

Representative Pramila Jayapal of Washington, the chairwoman of the Congressional Progressive Caucus, said that progressives would not require the Senate to pass the sprawling social policy bill before voting for the infrastructure bill, as they had previously stipulated. But she said that liberal lawmakers needed to see written text for the $1.85 trillion legislation, and receive assurances from Mr. Biden that the two Democratic holdouts in the Senate, Joe Manchin III of West Virginia and Kyrsten Sinema of Arizona, would vote for it. Ms. Jayapal also said progressives would insist on voting on both bills back-to-back.

The demand underscored how little trust progressive lawmakers have in the two centrist senators. Representative Juan C. Vargas, Democrat of California, said he trusted Mr. Biden, but Mr. Manchin and Ms. Sinema had not convinced him they supported the social policy framework.

A lawmaker close to Ms. Sinema insisted she does support it, but her statement on it equivocated, he said, because she refused to allow House Democrats to tie her support for the social policy measure to their votes for the infrastructure bill that she helped craft.

There is plenty in the framework for liberals to love. “We have the biggest investment in housing since the New Deal,” Ms. Jayapal said. “There’s a lot of really good things in this bill.”

But, she added, “we have to finish it.”

Her comments came after an emotional closed-door meeting, where lawmakers rose and vented their frustration that they were being asked to move ahead and vote on the infrastructure legislation without seeing the text of the social safety net, climate and tax increase package.

Speaker Nancy Pelosi joined the meeting but did not speak, according to lawmakers who attended, arriving as Representative Alexandria Ocasio-Cortez of New York was speaking, and taking a seat in the front row. Representative Mark Takano of California spoke next, and came close to tears as he explained how wrenching it was for him to be caught between his support for the speaker, who had called for a Thursday infrastructure vote, and his instinct that he was not ready yet to vote for the bill.

Asked by Ms. Jayapal if she wanted to speak, Ms. Pelosi responded that she just wanted to listen, according to two people familiar with the exchange. She left shortly after Ms. Bush delivered forceful remarks against voting for the infrastructure bill later that afternoon.

President Biden on Thursday proposed devoting $100 billion in his $1.85 trillion domestic policy bill to protect millions of undocumented immigrants, pushing to salvage a broader immigration overhaul that has stalled in Congress.

Democrats’ efforts to allow such measures to piggyback on the social safety net and climate legislation have so far fallen short, because of strict budget rules that limit what can be included.

House Democrats are planning to try to include one anyway, to appease colleagues who have said they cannot support a plan that lacks help for undocumented people, and to buy themselves time to devise an alternative that might be able to survive the Senate’s arcane rules.

Mr. Biden’s plan would recapture hundreds of thousands of unused visas dating back to 1992 and protect millions of undocumented immigrants who have lived in the United States for years from deportation. It also includes $2.8 billion for U.S. Citizenship and Immigration Services to more efficiently process migrants’ paperwork.

The Senate parliamentarian, the chamber’s top rules enforcer, has repeatedly shot down Democrats’ efforts to include such measures in the bill, which is moving through Congress under a special process known as reconciliation that shields it from a filibuster. Only provisions that directly impact government revenues can be included in such bills, and the parliamentarian has ruled that two other immigration measures do not pass that test.

House Democrats plan to include one of those disqualified plans in their bill: a date change to the immigration registry, which allows otherwise law-abiding undocumented immigrants who have been in the United States continuously since Jan. 1, 2011, to adjust their status and gain a pathway to citizenship.

They fully expect that the provision will be nixed by the parliamentarian, who has said the policy change far outweighed its fiscal impact. They plan to replace it later with a proposal costing about the same amount, once they find an alternative that can survive under Senate rules.

Senate Democrats have embraced a backup plan to expand the Homeland Security secretary’s authority to grant a temporary status known as parole to undocumented immigrants who have lived in the country for a decade, providing them with work permits and shielding them from deportation. The work permits would last five years, and then would need to be renewed for another five. The parliamentarian has not yet ruled on that proposal.

Immigration advocates cheered Mr. Biden’s decision to insist that an immigration overhaul be included in the reconciliation package as evidence they could achieve some aspects of reform while Democrats hold both chambers of Congress and the presidency.

“One way or another, we expect immigration reform to be in the final bill and win freedom for millions of immigrants,” said Lorella Praeli, co-president of Community Change Action.

The Biden administration has already made policy changes to immigration enforcement priorities that would make most of the people eligible for relief in the budget proposals a low priority for arrest and deportation. But those measures are far from permanent and can be reversed by another president.

Eileen Sullivan contributed reporting.

President Biden’s new social spending framework includes an expansion of health insurance that would provide millions of uninsured Americans with new coverage. But most of the health care programs that appeared in an earlier version of the proposal have been scaled back.

Notably, the revised plan does not include any provision to lower the prices of prescription drugs or the amount that older people with Medicare pay for costly medications.

Proposals to offer vision and dental benefits to Medicare recipients have also been eliminated, though the framework would establish new coverage for hearing aids.

The insurance expansion would provide generous subsidies to Americans who buy their own coverage, extending a temporary bump that was approved this year as part of the American Rescue Plan stimulus bill. The provisions offer free plans to many low-income Americans and new financial help with premiums to higher earners.

The plan would also offer subsidies and additional benefits to very low-income adults in 12 states, mostly in the South, that have declined to expand their Medicaid programs. Poor adults in those states, most of whom are currently ineligible for government aid for health coverage, would qualify for free private plans from the Affordable Care Act marketplaces that would charge minimal fees for doctor visits.

The enhanced subsidies and the Medicaid gap policies would expire at the end of 2025, according to a Democratic aide familiar with the negotiations and the text of a legislative draft released by the House Rules Committee on Thursday.

The plan would expand funding for home health services for older and disabled patients in the Medicaid program, many of whom are forced to seek care in nursing homes because of long wait lists for services at home.

The omission of a prescription drug provision has angered Democrats across the political spectrum. And the elimination of a Medicare dental benefit also disappointed many progressives, who had hoped that such a provision would improve public health and build political gratitude among older voters. But the dental benefit would have been expensive and taken several years to put in place.

All the details remain subject to negotiation and possible amendment as they make their way through the legislative process.

Senator Kyrsten Sinema of Arizona, a key centrist holdout, quietly struck an agreement with the White House on the Democratic promise to lower the cost of prescription drugs only to see the compromise drop out of the “framework” for social spending announced on Thursday by President Biden.

The decision left the Democratic architects of the compromise fuming that the White House had chosen the status quo of rising drug prices over a compromise that would have lowered costs, even if it only allowed the government to negotiate drug prices in an extremely limited way. And it also angered more progressive Democrats who were committed to reducing drug prices as part of their social spending bill.

Lowering prescription drug prices has been one of the most popular parts of the Democratic agenda, and was a key election theme for many congressional campaigns. But lawmakers have struggled to find an approach that can appeal to both progressive lawmakers, who want an aggressive approach to price regulation, and a handful of more centrist members, who are sympathetic to the drug industry’s concerns that price reductions could mean fewer jobs and less pharmaceutical innovation.

Representative Scott Peters, Democrat of California, whose legislation had served as a template for the discussions between Ms. Sinema and the White House, said the deal that was omitted from the President’s spending framework would have limited Medicare drug price negotiations to a small subset of outpatient medications, like chemotherapy drugs, that had passed their period of patent exclusivity.

But it also would have included limits on out-of-pocket expenditures by seniors, rebates for drugs whose prices rise faster than inflation, and a monthly cap of $35 for insulin, he said. Mr. Peters said that staying with the status quo “makes no sense at all.”

The compromise between Ms. Sinema and the White House was first reported by Politico. In discussions with the White House, Ms. Sinema successfully pushed to lower the monthly price cap on insulin from $50 to $35, Mr. Peters said.

The Peters bill would not allow Medicare to reduce the prices of most expensive medications. Prices for drugs that seniors buy at pharmacies would remain unaffected. And even most drugs administered by doctors would be ineligible for negotiation under the bill’s language.

The choice to remove any mention of prescription drug costs from the White House framework also disappointed legislators and lobbyists who favored a more expansive solution. Senators Bernie Sanders of Vermont and Amy Klobuchar of Minnesota both publicly expressed their disappointment.

Liberal Democrats vowed to keep pressing to include some version of the prescription drug proposal in the package. Senator Bernie Sanders of Vermont, the Senate Budget Committee chairman, called it “a real lacking” that it was no longer in the bill.

Senators are continuing to consider the Sinema proposal.

“I don’t want the American people to say look, once again, the drug companies won out or the insurance companies won out,” Mr. Sanders said. “I want the American people to say, you know what, on this occasion working families won.”

President Biden proudly trumpeted his Build Back Better legislative “framework” Thursday, but that document is a long way from being an actual piece of legislation. Frameworks cannot be enacted and signed into law, though it would certainly simplify the process if they could.

The White House outline laying out broad areas of agreement on complex issues such as universal prekindergarten and clean energy investment incentives is really just a shell that will need to be filled out with pages and pages of dense and technical language explaining exactly how the new programs will be implemented and who will qualify.

Adding an entire new benefit to Medicare is going to take more legislative language than just “allow Medicare to cover the cost of hearing,” as the framework declared.

Trying to satisfy progressive Democrats who insisted on seeing text of the social safety net bill before agreeing to end their blockade of a separate infrastructure measure, House Democratic leaders on Thursday afternoon released a 1,684-page preliminary version of their measure drafted by various committees.

But even that bill was more of a starting point for negotiation than a final product, cobbled together before Mr. Biden’s framework was unveiled. It most likely will take substantial revising to align it with the president’s vision and ultimately produce a final version that has the support to clear Congress.

Speaker Nancy Pelosi conceded the proposal would be undergoing changes once lawmakers got their hands on it.

“For those who said they want to see text, the text is there for you to review, for you to complain about, for you to add to or subtract from — whatever it is,” she told reporters. “We’ll see what consensus emerges from that.”

Whatever consensus does emerge, it will then have to be put in bill form and then pass both the House and Senate, a process that will take time as lawmakers haggle over the fine points.

While it may be trite to say the devil is in the details, that has long proved true about legislative language. Lawmakers who avidly support abstract concepts might balk at the details laid out in bill form. That is a main reason House progressives have been insisting that they see a bill before agreeing to move forward on the infrastructure measure they have been blocking for leverage over the social policy and climate measure.

A few words or a phrase can make a huge difference. Legislative wars have been waged over the difference between “may” and “shall.”

That also helps explain why the centrist Democratic Senators Joe Manchin III of West Virginia and Kyrsten Sinema of Arizona are refraining from declaring definitively that they will support the framework, since the legislation that emanates from it could go beyond what they would accept.

Mr. Manchin, for example, delayed a vote on a major Democratic pandemic relief bill this year over his unhappiness with the final language on unemployment benefits after the bill had already hit the floor and was on the runway to passage.

No language for the social safety net bill has even emerged in the Senate. But the good news for Democrats — and for beleaguered staff members who write legislation — is that much work has already been done in the committees and congressional offices that have championed particular provisions for years in some cases. Existing legislative proposals can be revised and tailored to fit in the framework and then compiled into what will undoubtedly be a voluminous piece of legislation at the end of the day.

But it will be legislation, not a framework, that gets passed on Capitol Hill — if anything gets passed at all.

President Biden announced Thursday a revised framework to try to pass a $1.85 trillion social safety net bill and a $1 trillion infrastructure measure, just hours before he planned to leave for a six-day European trip to meet with world leaders.

“After months of tough and thoughtful negotiations, I think we have — I know we have — a historic economic framework,” the president said. “This framework includes historic investments in our nation, and in our people.”

Mr. Biden delivered his remarks from the East Room of the White House after returning from Capitol Hill, where he pleaded with Democratic lawmakers to put aside their differences and vote for both measures as a way of advancing their common agenda.

“No one got everything they wanted, including me,” he said. “But that’s what compromise is. That’s consensus. And that’s what I ran on.”

For Mr. Biden, the announcement of the framework is a major step toward making good on the heart of his campaign promises: to invest in infrastructure, rebuild the social safety net, shrink the gap between the rich and poor and prove democracy can work.

Mr. Biden acknowledged that some parts of his agenda will not get done in the current round of legislation, including free community college and federal paid family leave.

“I know how deeply people feel” about their priorities, he said.

But he began what aides said will be a robust effort to sell the benefits of the plan to the American people, calling it a historic effort that will begin to fundamentally alter the way government provides services to the American public in the years to come.

In concluding his remarks, he urged lawmakers to “get this done” and took no questions from reporters.

“This agenda, the agenda that’s in these bills, is what 81 million people voted for,” he said. “Their voices deserve to be heard, not denied.”

As they hunt for revenue to pay for their sprawling spending bill and try to unite a fractured caucus, Democrats are attempting to rewrite the United States tax code in a matter of days, proposing the kind of sweeping changes to how America taxes businesses and individuals that would normally take months or years to enact.

The effort has effectively discarded trillions of dollars of carefully crafted tax increases that President Biden proposed on the campaign trail and that top Democrats have rolled out in Congress. Instead, lawmakers are throwing a slew of new proposals into the mix, including a tax on billionaires, hoping that they can pass muster both legally and within their own party.

On Thursday, the White House rolled out its own set of tax proposals, including a surtax on the wealthiest Americans and a new tax on publicly-traded companies that buy back their own shares.

The frantic attempt to overhaul the complex U.S. tax code remains in a state of flux given the disparate tax proposals being considered — and rejected.

On Wednesday, with Senator Joe Manchin III and some House Democrats expressed reservations about the tax on billionaires that was proposed earlier in the day by Senator Ron Wyden of Oregon. On Tuesday, Mr. Manchin shot down a plan that would have given the Internal Revenue Service more visibility into certain taxpayers’ bank accounts in order to catch tax cheats, forcing a group of Senate Democrats who support the provision to try to negotiate a compromise.

Mr. Manchin’s opposition to a new federal paid leave program also appeared to doom its chances of being included in the final legislation, although supporters of the provision said they would fight to keep it intact.

Senator Mark Warner, a Virginia Democrat, acknowledged on Wednesday that the rapid pace of the legislative process posed risks and said it would be preferable to “allow some of this very, very complicated tax policy to get an appropriate airing back and forth.”

The need to roll out new tax proposals stems largely from the concerns of business groups — and moderate Democrats — who effectively killed Mr. Biden’s initial plan to raise the corporate tax rate to 28 percent from 21 percent to pay for his clean energy and social policy initiatives. Other ideas proposed by the White House, including raising the top marginal rate for the wealthiest taxpayers and doubling the capital gains tax, have also been jettisoned.

The new policy proposals include elements of the kind of wealth tax that Mr. Biden shied away from during his campaign in favor of other tax increases. Under the new plan, billionaires, who often pay little to nothing in federal income taxes, would have to pay taxes on the increased value of certain liquid assets, like stocks and bonds, even if those assets were not sold and the gains were not realized.

But the White House did not throw its support behind that plan and instead proposed a surtax on the very rich. It would differ from the billionaires tax in that it would apply to income, rather than the value of liquid assets like stocks and bonds. Those with incomes exceeding $10 million would face a 5 percent tax and another 3 percent tax would be levied on those with incomes above $25 million.

A second proposal, which Mr. Biden also included in the new framework released on Thursday, would impose a 15 percent tax on companies that report at least $1 billion in profits to shareholders but have little or no federal tax liability as a result of tax deductions and other loopholes.

If enacted, the taxes would likely apply to fewer than 1,000 companies and individuals. But the breakneck speed at which changes are being considered and crafted is rattling business groups and some powerful Democrats, who have expressed concern about the consequences of moving so quickly.

The biggest legislative negotiation in years is taking place on Capitol Hill and at the White House, with key holdouts shuttling back and forth, lawmakers locked in intense private meetings and the news media providing minute-by-minute coverage of the developments.

And Republicans in the House and the Senate have absolutely nothing to do with any of it.

Sidelined by budget rules that give majority Democrats full control over the social safety net bill they are trying to push through, Republicans are strictly spectators as they revel in the internal Democratic disputes, snipe at the emerging legislation and game out how best to take advantage of the situation for next year’s crucial midterm elections.

Top Republican lawmakers who are usually mobbed by reporters walk unimpeded through the Capitol corridors while Democrats are chased down for any snippet of the current state of play. The lack of attention has not gone unnoticed.

“We’re a little bit surprised you’re even here today, because we know all the news is being made on the other side,” Senator Mitch McConnell, Republican of Kentucky and the minority leader, told reporters who showed up for his weekly news conference on Tuesday.

It is not an unprecedented situation. As recently as 2017, Republicans went it alone on their Trump-era tax cuts using the budget reconciliation process, which shields legislation from a filibuster, knowing that Democrats would not support the corporate tax breaks that the Republican Party was eagerly handing out. In 2009 and 2010, Democrats had substantial enough majorities in the Senate and the House that they could enact the Affordable Care Act on their own over universal Republican resistance.

Aware that Republicans would never support the kinds of social and climate programs they are trying to enact in the safety net legislation, Democrats are the ones using reconciliation this time. With the shoe on the other foot and with razor-thin Democratic majorities, the one-sided legislating has rendered Republicans virtually irrelevant as Congress debates potentially momentous legislation expected to cost at least $1.5 trillion.

“As somebody who is open to ideas from both sides and works on a lot of different initiatives with Democrats, to really not be involved or engaged in any aspect of it is just really odd,” said Senator Lisa Murkowski of Alaska, who is among the few Republicans who occasionally join with Democrats on important legislation.

But there seems to be no fear of missing out among Republicans, given their hostility to the emerging domestic policy package, which would lead to a level of social spending that is anathema to Republican lawmakers.

“They just have to satisfy their political base to the point where it gets pulled so far left,” Senator John Cornyn, Republican of Texas, said of the Democrats. “Obviously we don’t like being shut out of the policymaking, but that is the choice they made.”

The budget reconciliation process allows Congress to advance certain spending and tax bills on a simple majority vote, freeing lawmakers in the Senate from the 60-vote threshold most legislation must meet to be considered. Democrats are aiming to use the process to pass their sweeping social safety net and climate change measure, which carries much of President Biden’s agenda, in the face of united Republican opposition.

The process begins with a budget resolution, which establishes a blueprint for federal spending and directs congressional committees to write bills to achieve certain policy results, setting spending and revenue over a certain amount of time. Its name refers to the process of reconciling existing laws with those directives. Here are some key things to know about the legislative maneuver.

There are strict rules on what can be included.

While reconciliation allows senators to scale procedural and scheduling hurdles, it is also subject to strict limits that could constrain any package Democrats seek to pass.

In the Senate, the “Byrd Rule,” established by former Senator Robert Byrd of West Virginia, bars extraneous provisions — including any measure that does not change revenue or spending, that affects the Social Security program or that increases the deficit after a period of time set in the budget resolution. It is intended to ensure that the reconciliation process cannot be abused to jam through unrelated policies.

The rule’s name lends itself to a number of bird-related puns commonly used to describe the stages of the process. There is the “Byrd bath,” when the Senate parliamentarian scrubs and analyzes a bill for any provision that violates the rule if a senator raises a concern about a violation. Anything that does not survive the scrutiny is known as a “Byrd dropping” and is removed from the legislation.

Vice President Kamala Harris could overrule the parliamentarian, but that has not been done since 1975.

The legislative math is proving tough for Democrats.

A budget blueprint was advanced in August and committees have been working on drafting the reconciliation legislation, but centrist Democrats in the Senate who have balked at the $3.5 trillion price tag have created an impasse as party leaders try to negotiate a compromise.

Because Republicans have made it clear they are unified in their opposition, Democrats cannot afford to lose even one vote from their party in the Senate. In the House, the math is almost as challenging: If every representative voted, Democrats could afford to lose only three of their members.