WASHINGTON (AP) — Sen. Joe Manchin settled in at President Joe Biden's family home in Delaware on a Sunday morning in the fall as the Democrats worked furiously to gain his support on their far-reaching domestic package.

The two-hour-long session was the kind of special treatment being showered on the West Virginia senator — the president at one point even showing Manchin around his Wilmington home.

But months later, despite Democrats slashing Biden's big bill in half and meeting the senator's other demands, Manchin is no closer to voting yes.

In an extraordinary display of political power in the evenly split 50-50 Senate, a single senator is about to seriously set back an entire presidential agenda.

"We're frustrated and disappointed," said Sen. Dick Durbin, the majority whip. "Very frustrated," said another Democratic senator granted anonymity to frankly discuss the situation Thursday.

Biden said in a statement Thursday night that he still believed "we will bridge our differences and advance the Build Back Better plan, even in the face of fierce Republican opposition."

But with his domestic agenda stalled out in Congress, senators are coming to terms with the reality that passage of the president's plan, as well as Democrats' high-priority voting rights package, would most likely have to be delayed to next year.

Failing to deliver on Biden's roughly $2 trillion social and environmental bill would be a stunning end to the president's first year in office.

Manchin's actions throw Democrats into turmoil at time when families are struggling against the prolonged COVID-19 crisis and Biden's party needs to convince voters heading toward the 2022 election that their unified party control of Washington can keep its campaign promises.

The White House has insisted Manchin is dealing with the administration in "good faith," according to deputy White House press secretary Andrew Bates.

Manchin, though, has emerged as an uneven negotiator — bending norms and straining relationships because he says one thing one day and another the next, adjusting his positions, demands and rationale along the way.

Democratic senators have grown weary of their colleague, whose vote they cannot live without — but whose regular chats with Republican leader Mitch McConnell leave them concerned he could switch parties and take away their slim hold on power.

"Mr. Manchin and the Republicans and anybody else who thinks that struggling working families who are having a hard time raising their kids today should not be able to continue to get the help that they have, then that's their view and they've got to come forward to the American people and say, 'Hey, we don't think you need help,'" said Sen. Bernie Sanders, the independent from Vermont. "Let them tell the American people that."

The senator appears to both relish and despise all the attention he has commanded over many months at Biden's home in Delaware with Senate Majority Leader Chuck Schumer, in regular visits with Biden at the White House and in his daily strolls through the Capitol, where he banters amiably, swats back questions or simply clams up -- which becomes a statement of its own, leaving Manchin-whisperers to wonder what his silence means.

"I got nothing — n-o-t-h-i-n-g," he drawled to the reporters waiting outside the Democrats' closed door lunchroom Thursday as it became clear there would be no Christmas deal.

But between his endless hallway utterances is a consistent through-line in Manchin's months-long commentary about what he wants in — and out — of Biden's big package before giving his vote. The short version is he's not quite there yet.

Like the chief executive he once was — as governor of a state that surveys show ranked 47th in the nation for health care outcomes and 45th in education — Manchin ultimately decides where the attention goes next. And he has been effective.

So far, Manchin has gotten much of what he wanted: Biden halved what had been a $3.5 trillion proposal to $1.75 trillion, once Manchin gave his nod to that figure.

Manchin insisted the corporate tax rate Biden proposed raising to 28% would not inch past 25% — in fact, it ended up not being raised at all, thanks to opposition from another hold-out Democrat, Sen. Kyrsten Sinema of Arizona.

The coal-state senator insisted the new renewable energy incentives to fight climate change would not come at the expense of fossil fuels. The White House scrapped plans for a nationwide renewable energy standard that environmental advocates viewed as the most significant tool for curbing climate change.

And Manchin's demands for "no additional handouts" have limited some of the proposed social programs, and appear destined to tank plans to launch the nation's first-ever paid family and medical leave program for workers whose employers don't provide the paid time off to temporarily care for loved ones.

But what Manchin actually does want is much more unclear. And it all raises the question of whether Manchin even wants Congress to pass any "Build Back Better Act" at all.

For progressives, the stalemate Manchin engineered was exactly what lawmakers have feared after Congress signed off on a companion $1 trillion bipartisan infrastructure bill rather than force the two bills to move together to Biden's desk.

Rep. Rashida Tlaib of Michigan called it "tragic." Rep. Cori Bush of Missouri said, "We must not undermine our power as a government nor the power of the people by placing the fate of Build Back Better at the feet of one Senator: Joe Manchin."

Speaker Nancy Pelosi, who helmed Biden's latest compromise version to House passage, downplayed the Manchin negotiations as part of the process. "This is legislating," she said.

But this week, Manchin introduced a new demand, suggesting the enhanced child tax cut, which has been one of the most significant federal policies Democrats enacted this year — lifting some 40% of the nation's children from poverty — must run for the full 10 years of a traditional federal budget window rather than just one, as the House approved in a cost-cutting compromise.

It's a non-starter — the price of a decade-long child tax cut would consume the bulk of Biden's bill.

All this while Democrats also need support from Manchin, and Sinema, for Senate rules changes so they can overcome the 60-vote threshold needed to overcome a Republican filibuster to pass voting rights.

Manchin met with McConnell on Thursday, as they often do.

"As you know, he likes to talk," the Republican leader told reporters. "It would not surprise you to know that I've suggested for years it would be a great idea, representing a deep red state like West Virginia, for him to come over to our side."

McConnell added, "I don't think that's gonna happen."