Democratic Sen. Joe Manchin said Sunday he cannot back his party’s signature $2 trillion social and environment bill, seemingly dealing a fatal blow to President Joe Biden’s leading domestic initiative heading into an election year when Democrats’ narrow hold on Congress was already in peril.

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Manchin told “Fox News Sunday” that he always has made clear he had reservations about the bill and that now, after five-and-half months of discussions and negotiations, “I cannot vote to continue with this piece of legislation.” His choice of words suggested an openness to continuing talks, but all but said the bill would die unless it was reshaped to his terms.

In an unusually confrontational response to a senator whose vote is crucial, White House press secretary Jen Psaki called Manchin's statement “a sudden and inexplicable reversal in his position" and “a breach of his commitments" to Biden and congressional Democrats.

“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 legislation's apparent collapse is sure to deepen the bitter ideological divisions within the Democratic Party between progressives and moderates. That would call into question whether Democrats will be able to join together behind any substantial legislation before the November congressional elections. And it adds a note of chaos just as Democrats need to demonstrate accomplishments and show a united front before the fall campaign.

The bill carries huge investments for helping millions of families with children, including extending a more generous child tax credit, creating free preschool and bolstering child care aid. There’s assistance to help people pay health care costs, new hearing benefits for Medicare recipients and provisions limiting price increases on prescription drugs.

Also included are funds for caring for the elderly, housing, job training and more than $500 billion for tax breaks and spending aimed at curbing climate change. Nearly all of it would be paid for with higher taxes on the wealthy and large corporations.

Manchin's opposition puts it all on hold indefinitely. The West Virginia senator cited several factors weighing on the economy and the potential harm he saw from pushing through the “mammoth” bill, such as persistent inflation, a growing debt and the latest threat from the omicron variant.

“When you have these things coming at you the way they are right now, I’ve always said this ... if I can't go home and explain it to the people of West Virginia, I can’t vote for it," he said.

“I tried everything humanly possible. I can’t do it,” he said. “This is a no on this legislation. I have tried everything I know to do."

Though Manchin has been Democrats’ main obstacle all year to pushing the massive package through the narrowly divided Congress, his declaration was a stunning repudiation of Biden’s and his party’s top goal. A rejection of the legislation had been seen by many as unthinkable because of the political damage it could inflict on Democrats.

Sen Bernie Sanders, I-Vt., criticized Manchin for withdrawing his support and urged Democratic leaders to bring the bill to the floor anyway and force Manchin to oppose it.

“If he doesn’t have the courage to do the right thing for the working families of West Virginia and America, let him vote no in front of the whole world, “ Sanders told CNN’s ”State of the Union.”

It is rare for a member of a president’s own party to administer a fatal blow to their paramount legislative initiative. Manchin’s decision called to mind the famous thumbs-down vote by Sen. John McCain, R-Ariz., that killed President Donald Trump’s 2017 effort to repeal the health care law enacted under President Barack Obama.

“Infuriated,” said Rep. Jamaal Bowman, D-N.Y., among the progressives fighting for a more robust Biden bill.

“We’ve had concerns about trusting Joe Manchin throughout the year,” Bowman said by telephone on Sunday. “Manchin is the one that is killing Biden’s agenda.

Even more centrist lawmakers piled on, vowing to keep fighting for Biden’s bill.

“After months of negotiations, one Democratic U.S. Senator has now summarily walked away from productive negotiations. That is unacceptable, and we cannot act like this moment is the end,” said Rep. Abigail Spanberger, D-Va.

Last week, Biden all but acknowledged that negotiations over his sweeping domestic policy package would likely push into the new year. But the president had insisted that Manchin reiterated his support for a framework that the senator, the White House and other Democrats had agreed to for the flagship bill.

On Sunday, Manchin made clear those were Biden's words, not his own. The senator criticized fellow lawmakers for a bill that “hasn't shrunk” after he initially agreed to a $1.5 trillion framework and said social programs must be paid for over 10 years instead of just a few years to win his support, a nonstarter due to cost.

For instance, just extending the child tax credit program for the full 10-year budget window would cost well over $1 trillion. That would consume most of Biden’s bill, crowding out other key initiatives on health care, child care, education and more.

“We should be up front and pick our priorities,” Manchin said.

Democrats largely dismiss Manchin’s assertions that the bill would fuel inflation and worsen budget deficits. Democrats say it would put money in peoples’ pockets to help them afford rising prices, and that strengthening child care, education and job training would help people get back to work and find better jobs. That would increase productivity and help employers fill empty job slots, both of which would work to keep price increases in check.

A report from the nonpartisan Congressional Budget Office earlier this month said that if many of the bill’s temporary spending boosts and tax cuts were made permanent, it would add $3 trillion to the price tag. That would more than double its 10-year cost to about $5 trillion. Democrats has called the projections from the Republican-requested report fictitious.

But Democrats note that the CBO estimated that the legislation is almost completely paid for. Its tax boosts, more aggressive IRS collection of revenue from higher earners and other savings would add around $200 billion to federal deficits over the coming decade, CBO has estimated - a small percentage of the $12 trillion in red ink CBO had already projected.

By HOPE YEN and ALAN FRAM