Democrats are on the verge of a make-or-break moment – one that will determine the fate of Joe Biden’s ambitious economic agenda – as they rush to bridge the internal divisions threatening to derail passage of the sweeping social policy package and a smaller infrastructure bill.

Failure would be disastrous for the president and his party’s political prospects next year, but success was far from certain with less than 48 hours left before a consequential vote in the House on Thursday. In a sign of the stakes, Biden canceled a scheduled trip to Illinois to remain in Washington and “continue working on advancing these two pieces of legislation”, according to a White House official.

“This is a big week for the American people. It’s a big week for President Biden. It’s a big week for House and Senate Democrats,” the New York congressman Hakeem Jeffries, a member of House leadership, told reporters. “We’re not running away from that. We’re leaning into it. We embrace it. We understand that we’ve been given the opportunity to govern for the people, to build back better, that’s exactly what we are committed to doing.”

Democratic leaders publicly projected confidence as they toiled behind the scenes to craft a compromise proposal that satisfies the many demands and competing interests that have put its passage in jeopardy, notably the dogged opposition of two Democratic senators. With Republicans unified in their opposition, they will need the vote of every Democrat in the Senate and nearly every Democrat in the House.

“In the next day or so we hope to come to a place where we can all move forward on that,” the House speaker, Nancy Pelosi, told reporters on Tuesday at the Capitol. “We will pass both bills.”

Democrats broadly share Biden’s vision for his “Build Back Better” agenda, which includes a once-in-a-generation expansion of the nation’s social safety net and an overhaul of the tax code. But disputes remain over the particulars of the legislation, from its overall size to key measures combating climate change and expanding healthcare.

At the center of the uncertainty was a deal Pelosi made with moderates and progressives, to tie the infrastructure bill, which passed the Senate with bipartisan support and would fund roads, broadband and other infrastructure projects, to the far larger policy proposal, that would spend $3.5tn over the next decade on Democratic priorities such as climate change, healthcare and childcare.

After promising to hold a vote on both measures at the same time, Pelosi told her caucus that the House should proceed with passage of the infrastructure bill while the Senate attempts to reach a consensus on the spending plan, after a pair of moderate holdouts balked at its price tag. As they rushed to trim the bill, Pelosi indicated that the House would not take up a bill that didn’t have the support of all 50 Democrats in the Senate.

“The change in circumstance regarding the reconciliation bill has necessitated a change in our Build Back Better legislation but not in our values,” Pelosi wrote in a letter to Democrats on Tuesday.

Nevertheless, she signaled that the House would move forward with a vote on the infrastructure bill on Thursday.

Progressives were furious about the change of strategy, with some calling it a “betrayal”. Several members of the Congressional Progressive Caucus said the planned to oppose the infrastructure bill on Thursday unless there was also a vote on the the $3.5tn legislation.

“Progressives will vote for both bills, but a majority of our members will only vote for the infrastructure bill after the president’s visionary Build Back Better Act passes,” congresswoman Pramila Jayapal of Washington, the caucus chairwoman, said in statement after surveying her 96 members on Tuesday.

Progressives in the Senate were also frustrated, saying that they only supported the infrastructure bill because of the understanding that the measures would be tied together in the House. Urging House progressives to hold the line, Senator Bernie Sanders warned that allowing the bills to advance separately would “end all leverage that we have to pass a major reconciliation bill”.

“That means there will be no serious effort to address the long-neglected crises facing the working families of our country, the children, the elderly, the sick and the poor,” he said. “It also means that Congress will continue to ignore the existential threat to our country and planet with regard to climate change.”

If Democrats can pull it off, the legislation has the potential to be transformative for millions of American families. It would extend the child tax credit, establish universal pre-k, create a federally paid family and medical leave system, in addition to an array of programs to combat climate change and transition the country toward renewable energy. The plan would be paid for by trillions of dollars in tax increases on the wealthiest Americans and corporations.

Biden has said that the total cost of the bill is actually “zero” since it will be offset by an increase in tax revenue over several years.

Republicans have decried the scale of Biden’s spending and tax plan, saying that it would stifle economic growth and worsen the nation’s debt.

“This spending is on a scale not seen before in our country,” said the Republican senator John Barrasso of Wyoming, hoisting a copy of the 2,465-page draft legislation. “This bill represents Bernie Sanders’ socialist dream.”

Amid the impasse, Biden held a series of meetings at the White House on Tuesday with Senators Joe Manchin of West Virginia and Kyrsten Sinema of Arizona over their objections to the cost of his agenda.

“There was no commitments made at all,” Manchin told reporters on Capitol Hill, after his meeting with the president. “Just good negotiations.” He said he had not given Biden a proposed topline figure.

“This is clearly a pivotal moment,” the White House press secretary, Jen Psaki, said, describing the president as “deeply engaged” with Democratic leaders and members to pass his agenda.

“He’s working together in lockstep with Speaker Pelosi and Leader Schumer to get this done,” she said. “And they are all clear-headed … about the challenge of what we are pressing to achieve this week.”

With Biden’s economic agenda hanging in the balance, Democrats are also scrambling to avert a government shutdown and avoid a financial crisis with the national debt, after Republican senators blocked a measure that would have funded the federal agencies and raised the country’s borrowing limit.

Speaking on Capitol Hill on Tuesday, the treasury secretary, Janet Yellen, warned lawmakers that the consequences of failing to raise or suspend the debt limit would be “catastrophic”. Without congressional action, she said the treasury department will struggle to pay its bills on 18 October.

Hours later, Senate Republicans rejected a second attempt by Democrats to raise the debt ceiling, this time using a procedural maneuver to avoid a filibuster.

Can Democrats salvage Biden’s agenda, keep the federal government open and avert fiscal calamity?

“You know me, I’m a born optimist,” Biden said on Monday, as he rolled up his sleeve to receive a Covid-19 booster shot. “We’re gonna get it done.”