Negotiations between the White House and top Democratic lawmakers intensified Tuesday as President Biden scrambled to save roughly $4 trillion in economic initiatives from an embarrassing setback at the hands of his own party.

For Biden, the day of diplomacy sought to blunt a fast-worsening congressional stalemate: An upcoming House vote on a $1 trillion plan to improve the nation’s infrastructure remains imperiled as Democrats clash over the size and scope of a second spending package.

Liberal-leaning House Democrats hope to spend as much as $3.5 trillion in that bill in a bid to remake federal health-care, education and climate laws, financed chiefly through tax increases. But some moderates, led by Sens. Joe Manchin III (D-W.Va.) and Kyrsten Sinema (D-Ariz.), have continued to reject the price tag and policy scope of the measure, frustrating their Democratic counterparts on Capitol Hill.

To try to break the logjam, Biden huddled with the two centrists in a series of meetings at the White House on Tuesday. But their negotiations did not immediately appear to produce an agreement over the final size of the spending package, frustrating liberals who have pledged in the absence of a deal to scuttle a vote on the infrastructure package expected in the House later on Thursday.

“We articulated this position more than three months ago, and today it is still unchanged,” said Rep. Pramila Jayapal (D-Wash.), the leader of the roughly 100-member Congressional Progressive Caucus.

The uncertainty later prompted Sen. Bernie Sanders (I-Vt.), the leader of the chamber’s Budget Committee and the chief architect of the $3.5 trillion spending plan, to encourage House Democrats to take a stand. He urged them to vote against the infrastructure bill to preserve their “leverage” in securing their other spending priorities in talks with centrists including Manchin and Sinema.

“This has gone on month after month after month. It seems to me, and I may be wrong on this, but it seems we’re no further along than we were several months ago,” Sanders lamented in a later interview.

The flurry of activity reflected the increasingly delicate dance facing Biden, House Speaker Nancy Pelosi (D-Calif.) and Senate Majority Leader Charles E. Schumer (D-N.Y.), as they seek to craft what could become one of the largest bursts of spending in U.S. history. And it illustrated the harsh reality of Democrats’ own majorities in Washington, which are as powerful as they are limited, requiring party leaders to tread carefully to avoid angering powerful blocs of lawmakers.

In a sign of trouble, Biden canceled a planned trip to Chicago on Wednesday. An administration official, speaking on condition of anonymity to describe the plans, said the president would focus instead on advancing the two now-stalled economic initiatives he supports on Capitol Hill.

The fate of Biden’s agenda is not even the most urgent problem Democratic leaders face: The party’s lawmakers also are staring down a series of looming, critical fiscal deadlines starting this week. Congress must fund the government by Thursday night or risk a partial shutdown starting Friday morning. And it must adopt a separate measure that preserves the country’s ability to borrow to pay its bills before mid-October. Treasury Secretary Janet Yellen told Congress on Tuesday that her agency would run out of flexibility to avoid missing payments after Oct. 18, potentially thrusting the U.S. into an unprecedented financial crisis.

As Biden tried to quell his party’s internal rebellion, Schumer worked to resolve a partisan fight over the debt limit. But Senate Republicans blocked Democrats on Tuesday from advancing a bill that would address the issue, a day after the GOP thwarted a similar debt ceiling proposal that also would have funded the government. Speaking for his party, Senate Minority Leader Mitch McConnell (R-Ky.) opposed raising the country’s borrowing limit as part of a broader strategy to battle back Biden’s spending initiatives.

In doing so, McConnell also repeated Tuesday his position that Democrats should rely on a legislative process known as reconciliation to advance an increase in the debt ceiling. Such a tactic would require the support of every Democrat in the chamber — while still allowing Republicans to oppose it — in order for the country to avoid a default. But the maneuver could be time consuming and politically costly, a reality Schumer acknowledged as he rejected it as “risky” — resulting in a stalemate that now leaves Washington two days from shutdown and just under three weeks from default.

In the meantime, the clock continued to tick on a central element of Biden’s agenda. On the very day that federal funding expires, the House is also set to vote on an infrastructure plan that passed the Senate on a bipartisan basis last month. But the vote, which should have been an uncomplicated affair, increasingly remains in great doubt — as Democratic factions snipe at each other over the future of their shared agenda.

The president labored to address the most significant logjam Tuesday, huddling privately with Manchin and Sinema at the White House to discuss the up-to $3.5 trillion tax-and-spending plan. The discussions were significant, since some left-leaning Democrats say they need the two pivotal centrists to commit fully to a price tag before they are willing to loosen their blockade on infrastructure.

But neither Manchin nor Sinema exited their conversations with the president offering a clearer commitment as to how much spending they would support. As he returned to the Capitol, Manchin instead described it as an “ongoing process,” telling reporters: “We really are working.”

The behind-the-scenes wrangling has proven to be high stakes for Democrats, since the final cost ultimately determines what lawmakers can include in a bill they have repeatedly described in historic terms. The proposal as it stands aims to expand Medicare coverage, combat climate change, offer universal prekindergarten and authorize a bevy of new or expanded aid to families with children, delivering a set of programs that many in the party promised on the 2020 campaign trail

In private meetings and public comments, Democratic leaders across the party’s ideological spectrum already have come to acknowledge they cannot adopt a measure as large as they initially had hoped. But they still have a significant gap to bridge, since some liberal Democrats believe Sinema has told Biden she supports less than $2 trillion in total spending, according to three Democrats familiar with the matter who requested anonymity to describe the talks. Manchin similarly has called for sweeping cuts to the initial plan that House Democrats produced earlier in September.

Sinema declined to comment. A White House official, who spoke on the condition of anonymity to describe the president’s discussions, said Biden also has been in touch with progressives in recent days as part of a wide-ranging outreach campaign to pass his political agenda on Capitol Hill.

Pelosi, meanwhile, has projected political optimism, stressing on Tuesday that Democrats are “making some good progress” at resolving their differences. And moderate lawmakers, who helped orchestrate the looming, uncertain Thursday vote on infrastructure spending, said they still expect to prevail when the package comes to the floor.

“I believe at the end of the day, people will vote yes,” said Rep. Josh Gottheimer (D-N.J.), who helped spearhead the agreement securing the date. “I just don’t believe people are going to hit the ‘no’ button.”

Some lawmakers confide they are likely to end up with a package in the low-to-mid $2 trillion range. The looming potential for deep cuts to their original proposal has prompted some Democrats in the meantime to attempt and wall off their favorite provisions.

A group of Democrats led by House Majority Whip James E. Clyburn (D-S.C.) on Thursday, for example, stressed that the party needed to expand Medicaid as part of their upcoming package, hoping to stave off cuts in health-care provisions that count among the most expensive in the still-forming bill.

A wide-ranging group of liberal lawmakers, led by Reps. Mondaire Jones (D-N.Y.), Mikie Sherrill (D-N.J.) and Katie Porter (D-Calif.), sent their own letter last week to protect billions of dollars in new child-care assistance, citing the hardships many working parents faced during the pandemic. Still a third group including Alexandria Ocasio-Cortez (D-N.Y.) wrote a missive to “strongly urge” Democratic leaders to preserve $30 billion for a civilian climate corps that might allow young people to help fight global warming.

One of the potential cuts already in lawmakers’ crosshairs involves a plan to provide free community college to all Americans, a widely supported plan that House Democrats included in the tax-and-spending bill they drafted earlier this month. Sinema and other centrists would like to see the program restricted to those at lower incomes, the sources said, part of a broader campaign by moderates to more narrowly target aid programs that had been proposed in a universal manner.

In other cases, centrist Democrats including Manchin and Sinema have sought to scale back eligibility criteria, limiting the number of Americans who can obtain the aid in the first place. Manchin has focused much of his effort on the child tax credit, seeking to impose new work and education requirements that many within his own party have opposed as unworkable. His office did not respond to a request for comment.

The disputes over the package’s total cost are only part of the challenge these Democrats face, as party lawmakers struggle to work through internal divisions over a wider array of fights — from how to lower the cost of prescription drugs to the best way to battle climate change. Pharmaceutical giants and energy lobbyists have further descended on the debate, adding to Democrats’ anxieties at a time when much of the economic package is coming together outside of public view.

“You have the pharmaceutical industry spending a fortune to make sure we don’t have lower prescription drug prices. … You’ve got the fossil fuel industry spending a fortune, making sure we don’t tap into their profits as they destroy the planet,” Sanders lamented earlier Tuesday. He said lawmakers needed to “stand up to the powerful special interests that dominate Congress,” adding it is “the challenge we face right now.”

Annie Linskey contributed to this story.