Sen. Joe Manchin III started his Tuesday in a downtown hotel ballroom, trading stories with one of Washington’s richest men in front of a crowd of hundreds of business leaders, journalists and fellow politicians all scrutinizing his every utterance for fresh clues about the fate of the pending trillion-dollar legislation pushed by President Biden.

Afterward, he arrived at the Capitol greeted by television cameras, and when he strolled to his office a few hours later, he was accompanied — as is now typical — by a chaotic pack of reporters pressing for news and a clutch of climate activists demanding he abandon his fossilfuel-friendly views.

Later — again in the full view of reporters — he huddled in the Senate basement with his chief antagonist, Senate Budget Committee Chairman Bernie Sanders (I-Vt.), who has been sharply critical of Manchin’s effort to slash his $3.5 trillion spending framework by more than half.

Manchin (D-W.Va.) ended the day much as he started it — in the spotlight and at the height of his power as a one-man pivot point for an all-Democratic government and a self-styled emergency brake on what he has increasingly characterized as a liberal agenda run amok.

“This position, I guess, I wouldn’t wish it on anybody,” he told billionaire Carlyle Group co-founder David Rubenstein at the morning event staged by the Economic Club of Washington — a remark that skimmed over just how eagerly and thoroughly he has sought to shape Biden’s legislative agenda to his liking.

Manchin is not alone in using his leverage to shape the pending legislation: Sen. Kyrsten Sinema (D-Ariz.) has delivered equally thorny ultimatums, albeit behind closed doors, and dozens of other lawmakers are looking to put a personal stamp on the must-pass domestic policy bill.

But none have turned their influence into public spectacle the way that Manchin has this year, and none have openly sought to distance themselves from their party label as the West Virginian has. Now — with Democrats eager to strike a deal before Biden leaves for Europe this week — Manchin’s machinations have reached a crescendo.

Manchin spent his Sunday morning at Biden’s home in Wilmington, Del., hashing out fine details over breakfast with the president and Senate Majority Leader Charles E. Schumer (D-N.Y.).

Then on Monday, he darted from meeting to meeting, including on climate policy — where Manchin, chairman of the Senate Energy and Natural Resources Committee, has already scaled back Democratic decarbonization plans — and then to a private room at Cafe Milano, the Georgetown power den, where he declared himself “totally out of sync” with his party to a group of corporate bigwigs.

“I’m just trying to survive in a very, very, very divided Congress and a very divided country,” he said there, according to accounts from NBC and Politico reporters who attended the dinner, after declaring himself “totally out of sync” with fellow Senate Democrats. “And I don’t know how this is going to work out, guys. I really don’t.”

Describing his political philosophy to Rubenstein on Tuesday, Manchin said that while government has a “moral responsibility to take care of those who can’t take care of themselves,” it “should be my partner, not my provider.” Where private industry is willing and able to step in, he said, government should step back.

While those views may be out of step with an increasing liberal Democratic Party, Manchin also delivered a general vote of confidence in its de facto leader: “I support Joe Biden. I really think he was the right person at the right time. We just got to balance things out.”

Manchin has weighed in on virtually every aspect of the sprawling domestic policy bill known as Build Back Better that represents Biden’s best chance to enact major legislation ahead of the 2022 midterms.

A power utility penalty-and-incentive framework known as the Clean Electricity Performance Program has already been discarded because of Manchin’s opposition, and other climate provisions — including a methane tax — appear to be on the chopping block. Sen. Kirsten Gillibrand (D-N.Y.) and others scrambled this week to salvage a paid family leave program after Manchin balked, while his objections threw plans to expand Medicare and Medicaid into serious doubt.

On Tuesday, Manchin threw a new wrench into the gears when he announced at the Economic Club event that he had single-handedly vetoed a key Democratic proposal to increase tax revenue by requiring banks to report a much wider swath of financial activity to the IRS. That would give the federal government powerful new tools to combat tax evasion, potentially raising hundreds of billions of dollars over the coming decade for spending proposals, but it has fueled political attacks from Republicans who say it amounts to IRS “snooping” in innocent taxpayers’ bank accounts.

Manchin said he told Biden in the Sunday meeting that any such reporting requirement — even restricted only to accounts of $10,000 or more — would be a red line.

“I said, ‘Do you understand how messed up that is? To think that Uncle Sam’s going to be watching?’ ” he told Rubenstein. “And so [Biden] says, ‘I think Joe’s right on that.’ So I think that was going to be gone.”

The declaration hit Capitol Hill as yet another bolt from the gods — a surprise attack from a mercurial lawmaker who, to some colleagues, has randomly swung a meat ax at their policy agenda.

Manchin, however, has toed the party line on other aspects on the package. He has supported increasing tax rates for corporations and wealthy individuals, and he is also backing an effort to force pharmaceutical companies to negotiate with Medicare over the billions of dollars in costs that taxpayers foot annually for prescription drugs. (It’s Sinema, not Manchin, who has thrown those provisions into doubt.)

For some liberal Democrats, the fact that a single senator has been able to rein in what they and Biden have billed as a once-in-a-lifetime chance to address the climate crisis and improve the lives of poor and middle-class Americans has been a bitter letdown.

“I think we’ve given, you know, a lot of oxygen to that, and I don’t think we’re giving enough oxygen and daylight to the hardship and the struggles that the American people are experiencing right now,” Rep. Ayanna Pressley (D-Mass.) said when asked about Manchin’s influence.

But others have been more forbearing of the 74-year-old former West Virginia governor, who spent three decades navigating though Mountain State politics before succeeding the late Robert C. Byrd in 2010 — and adhering to a backslapping, aisle-crossing approach to business in a chamber where power was increasingly wielded only through sharp-edged partisan tactics.

During Donald Trump’s presidency, for instance, Manchin voted to confirm more Trump Cabinet nominees than any other Democrat and, at least for a time, entertained voting for Trump’s tax-cut bill. He’s a fixture of bipartisan “gangs” that have assembled to tackle sticky issues, and he’s firmly opposed changing Senate rules to sideline the minority party. The approach has allowed Manchin to win three elections in what has become an overwhelmingly Republican state, one that voted for Trump over Biden by 39 points in 2020.

“We’ve known that Joe has differences with the rest of the caucus. None of this is a big surprise,” Sen. Chris Murphy (D-Conn.) said. “I mean, is it frustrating to have no margin of error in a 50-vote majority? Sure. But I think all of us knew what we were in for.”

Manchin’s eagerness to chip away at his own colleagues’ legislative priorities — and his increasingly prominent status as a nemesis of the political left — has fueled new speculation that he might abandon the Democrats altogether. Similar rumors swirled during the Trump administration, when Manchin was briefly considered for a Cabinet post, Democrats were stuck in the Senate minority and Republicans were eager to pad their thin majority.

Following a report in Mother Jones magazine that he had discussed a potential party switch, Manchin acknowledged last week that he offered to become an independent — like Sanders and Sen. Angus King of Maine — while continuing to caucus with Senate Democrats, only to be dissuaded by his colleagues.

In fact, Manchin has made clear in his deeds and words that he would be no more comfortable as a Republican than he is as a Democrat. During Trump’s presidency, he was sharply critical of the party’s efforts to repeal health-care coverage and cut taxes on the rich. He twice voted to impeach Trump and has expressed deep qualms about the Jan. 6 attack on the Capitol — and the refusal of GOP leaders to support an independent commission to investigate it.

“Do you think by having a D or an I or an R is going to change who I am?” he told Rubenstein on Tuesday. “I don’t think the R’s would be any more happier with me than the D’s are right now.”

Jacqueline Alemany contributed to this report.