Sen. Joe Manchin III (D-W.Va.) on Sunday said he could not support Democrats’ roughly $2 trillion bill to overhaul the country’s health care, education, climate, immigration and tax laws, dealing a potentially insurmountable political blow to the final piece of President Biden’s economic agenda.

The statement of opposition was the most forceful condemnation yet from the moderate Democratic holdout, who cited rising consumer prices, a growing federal debt and the arrival of a new coronavirus variant as reasons he could not supply his must-have vote.

Democrats across the Capitol quickly blasted Manchin, arguing that he had failed to negotiate in good faith, especially since Biden had painstakingly scaled back his original ambitions to win the senator’s support. Illustrating its fury, the White House publicly attacked Manchin in an unusually personal statement, alleging he had misled the president in their private talks.

The political collision ultimately amounted to a death knell for the long-stalled proposal, at least in its current form. It also threatened to carry immediate economic consequences, since lawmakers had hoped as part of the proposal to extend a soon-expiring federal program that provides payments to more than 35 million American families with children.

The chain of events began early in the day, when Manchin appeared on “Fox News Sunday” and outlined his opposition to the proposal known as the Build Back Better Act, which borrows its name from Biden’s own 2020 campaign pledge.

“I can’t move forward. I cannot vote to continue with this piece of legislation, I just can’t,” he said.

“I tried everything possible,” Manchin added. “I can’t get there. … This is a no.”

In a separate statement, issued later Sunday, Manchin signaled that he still could continue negotiating with Biden and other top Democrats on a scaled-back version of the bill. But the senator otherwise said he could not “vote to move forward with this mammoth piece of legislation.” He said the effort would “dramatically reshape our society in a way that leaves our country even more vulnerable to the threats we face,” explaining that the country’s rising debt would complicate its ability to respond to “geopolitical uncertainty.”

The comments appeared to come as a shock to the Biden administration, which has argued that the package is paid for in full. In a lengthy rebuttal, White House press secretary Jen Psaki said the senator’s remarks appeared “at odds with his discussions this week with the President, with White House staff, and with his own public utterances.”

“If his comments on FOX and written statement indicate an end to that effort, they represent a sudden and inexplicable reversal in his position, and a breach of his commitments to the President and the Senator’s colleagues in the House and Senate,” she said.

Biden had sought to assuage Manchin’s concerns in recent weeks, speaking privately with the centrist Democrat in an attempt to win his vote. The talks marked a last-ditch effort in the waning hours of the year to dislodge a long-delayed measure that aims to expand Medicare benefits, lower prescription drug prices, authorize prekindergarten for all American children, invest new sums to combat climate change, and provide a slew of new financial support to help low-income Americans.

But the discussions repeatedly stalled, as Manchin continued to demand significant changes to the size and scope of the spending package, threatening the ability of Democrats to deliver on many of the promises they made on the 2020 campaign trail. The stalemate earlier in the week forced party leaders to abandon their plan to hold a vote on the bill before Christmas, with the hopes of returning to the debate next year.

Some Democrats still saw an opportunity for lawmakers to act swiftly come January. On Sunday, though, Manchin’s intensified opposition to the bill appeared to dash those hopes as well. Without his support, Senate Democrats simply cannot move the sprawling measure through the narrowly divided chamber even using the process known as reconciliation. The intricate legislative tactic allows the party to bypass a guaranteed Republican filibuster, but only if all Democrats — including Manchin — stay united.

The White House joined with other party lawmakers in promising to continue pushing their spending proposal once lawmakers return to Washington in January. But the shape of their efforts appeared destined to be much smaller and less sweeping than what many in the party initially sought, as they reckon again with a recalcitrant member of their own ranks whose fiscal conservatism has vexed them all year.

“Today, Senator Manchin has betrayed his commitment not only to the President and Democrats in Congress but most importantly, to the American people,” said Rep. Pramila Jayapal (D-Wash.), whose left-leaning bloc, the Congressional Progressive Caucus, advocated fiercely for the bill.

“He routinely touts that he is a man of his word, but he can no longer say that,” she said. “West Virginians, and the country, see clearly who he is.”

In 2021, Sen. Joe Manchin III (D-W.Va.) changed his top line spending number for President Biden’s agenda more than half a dozen times. (JM Rieger/The Washington Post)

For Democrats, Sunday’s developments marked the unfortunate climax in a debate that could have grand implications for their prospects in the 2022 midterm elections. It revealed the ideological fissures within the party and the limits of Biden’s own prowess as a negotiator, after the president spent months trying to coalesce allied lawmakers around a shared economic vision that they could sell to voters next November.

The saga began in the spring, when Biden first unveiled two spending blueprints to improve the nation’s aging infrastructure while providing new aid to families struggling financially nationwide. The size and scope of that second spending package, eventually valued at roughly $3.5 trillion, immediately troubled Manchin — and prompted Democrats to embark on a months-long process to whittle their policy aspirations down to a size he would support.

Party lawmakers soon clawed back not only the cost of their proposal but also its vast policy scope, seeking to woo Manchin at times by shelving entire provisions, including those that aimed to combat climate change and provide millions of Americans with paid family and medical leave. The changes left many Democrats uncomfortable, and it never quite satisfied the senator, who began in the fall to call on lawmakers to “pause” the legislative process.

Fearful that Manchin might walk away from the negotiations, liberal-leaning lawmakers in the House sought at the time to force his hand. For months, they pledged to hold up the infrastructure package, a bipartisan spending measure the moderate senator did support, to preserve the thrust of the Build Back Better Act. But most liberals ultimately loosened their grip in November, acceding to Biden’s requests to adopt the bipartisan measure to improve the nation’s roads, bridges, pipes, ports and Internet connections. Weeks later, House Democrats gave a green light to a scaled-back, roughly $2 trillion version of the Build Back Better Act, overcoming their own internal moderate revolt.

From there, though, Manchin only ramped up his criticisms.

With Biden’s backing, Democrats chose in the 10-year spending plan to stagger start and ending dates of many of its policy components, an attempt to lower its costs while ensuring it does not add to the deficit. But Manchin described that approach as a gimmick meant to hide its true cost.

Manchin demanded in recent weeks that every part of the Build Back Better Act must be funded over the full decade period, while keeping its price tag under $1.75 trillion. The condition essentially rendered it impossible for Democrats to preserve the breadth of their package and adopt even the ideas that are popular within the party, including an extension of expanded federal child tax benefits, which on its own could cost into the trillions of dollars.

In staking his position, Manchin essentially sided with Republicans, who have claimed the bill could cost trillions of dollars more than Democrats say. The stalemate led Biden personally to acknowledge on Thursday that it could still be “weeks” before the two sides could finalize an agreement — until Manchin on Sunday outlined his wide-ranging opposition to the bill.

“I cannot take that risk with a staggering debt of more than $29 trillion and inflation taxes that are real and harmful to every hard-working American at the gasoline pumps, grocery stores and utility bills with no end in sight,” Manchin said in his statement.

Republicans on Sunday quickly delighted in the news. Sen. Lindsey Graham (S.C.), the top GOP lawmaker on the chamber’s budget committee, praised Manchin and stressed in a statement that lawmakers must “focus on roaring inflation, particularly in the energy sector, as well as a broken supply chain, and potential threats coming from the new coronavirus variant.”

The White House, meanwhile, issued a lengthy rebuttal. In her statement, Psaki channeled the concern among administration officials that the senator had reneged on their talks, first approaching Biden with a potential deal before appearing to walk away Sunday.

In doing so, she also contested Manchin’s most pointed criticisms. Psaki said that economists have found the roughly $2 trillion proposal would not worsen inflation but rather ease some of its pressures. She stressed that the new spending would be financed in full through changes to federal tax policies, ensuring it adds nothing to the deficit. And she said the Biden administration would not abandon its push to see the bill become law.

“Just as Senator Manchin reversed his position on Build Back Better this morning, we will continue to press him to see if he will reverse his position yet again, to honor his prior commitments and be true to his word,” she said.

The White House saved its harshest condemnation of Manchin for his decision’s impact on the child tax credit, which Democrats expanded as part of a coronavirus stimulus law enacted earlier this year. The program pays out monthly sums to families with children, though it is set to expire at the end of December unless lawmakers take action in the coming days — a deadline that now seems impossible to meet given the stalemate over the broader bill.

“Maybe Senator Manchin can explain to the millions of children who have been lifted out of poverty, in part due to the Child Tax Credit, why he wants to end a program that is helping achieve this milestone — we cannot,” Psaki said in her retort.

The uncertainty left some congressional Democrats feeling that they had been duped by one of their own — the latest in a line of schisms with Manchin, who at various turns has opposed the party’s plans to provide coronavirus aid, address climate change, and overhaul election and voting laws.

“I am deeply saddened in this moment because much-needed resources we have fought all year for, that we have fought for decades for, are not coming,” Rep. Jamaal Bowman (D-N.Y.) said Sunday.

Bowman had joined a camp of lawmakers in the Congressional Progressive Caucus who voted against the infrastructure bill earlier this year to preserve it as leverage in talks with Manchin.

“We were concerned that Manchin and others weren’t negotiating in good faith,” Bowman said on Sunday. “And that’s exactly what’s playing out in real time.”

Amy B Wang contributed to this report.