For months, it has been one of the biggest questions in Washington: What does Senator Joe Manchin want?

Mr. Manchin, a West Virginia Democrat, fashions himself as an old-school centrist dealmaker, the sort of nearly extinct congressional species who hashes out deals over the bootleg moonshine he keeps stocked in unmarked Mason jars in his Senate office.

Like nearly all other senators who first served as a governor, he often bemoans the fact that he’s no longer a chief executive, with a security detail and the ability to make things happen on command. He created a former governors’ caucus in the Senate for like-minded colleagues and has often said his best day as a senator was worse than his worst day as governor.

Mr. Manchin, who was a quarterback at West Virginia University before injuries derailed his athletic career, enjoys the national spotlight and seeming nonstop attention from reporters, fellow senators and presidents too much to have sought a return to the Statehouse in Charleston.

The combination of his desire to make deals, create action and remain the center of political attention culminated over the weekend when he shocked Democrats, the White House and journalists with his announcement — on “Fox News Sunday” — that he would not support President Biden’s social policy agenda, a $2.2 trillion spending bill known as the Build Back Better Act that has served as the primary vehicle for his party’s agenda for 2021 and 2022.

Like his centrist Democratic colleague Kyrsten Sinema, who has also built a carefully crafted image as a senator who wants to get things done, Mr. Manchin finds himself at the center of competing priorities. He is the primary roadblock to the centerpiece of Biden’s domestic agenda, but as the deciding vote in a 50-50 Senate he is also the central figure with the power to create action.

As long as that’s the case, an unending cascade of attention will follow from the White House, fellow congressional negotiators and reporters, who for weeks have trailed Mr. Manchin around the Capitol like a pack of hungry dogs.

To figure out whether Mr. Manchin’s “no” is really a “no,” or, as is often the case in Washington, a “not yet,” I called Jonathan Kott, who worked as Mr. Manchin’s conduit to the news media from 2012 to 2019 and is now a lobbyist deciphering the senator’s thoughts for corporate clients.

“Joe Manchin is always up for discussing ways to get to ‘yes’ and how to make a bill better,” Mr. Kott told me. “It’s who he is. He’s a governor at heart. It’s how he negotiated with the State Legislature in West Virginia. I don’t know what the status of this bill is, but I know that Joe Manchin is always open to negotiations in honest and straightforward ways.”

So what, I asked, does that mean for the status of the Build Back Better legislation? What would Mr. Manchin agree to?

“He has told everybody what he wants,” Mr. Kott said. “Joe Manchin is pretty upfront and honest about what he wants, and he’s been saying it for six months.”

Indeed, unlike Ms. Sinema, who went silent before taking a public victory lap after Mr. Biden signed the infrastructure bill last month, Mr. Manchin is a regular talker in the Senate hallways and a fixture on the Sunday talk shows.

On Monday morning, he spent 15 minutes talking to Hoppy Kercheval, whose call-in radio show in West Virginia is perhaps the best gauge of the state’s politics.

There, Mr. Manchin lamented the very public pressure campaign to get him to agree to the social policy legislation and laid out in some detail why he remained opposed to it. He’s concerned about the national debt and spending, the senator said, and wants benefits like the federal child tax credit targeted to the poor and the middle class, rather than to all Americans.

(It is worth noting that proponents of the tax credit for all say inserting an income cap will mean that the benefit won’t go to as many poor people as need it, and that work requirements would by their nature cut out millions of those in poverty who could otherwise be helped.)

Mr. Manchin said that pressure campaigns hadn’t worked on him, and that he wouldn’t change his mind.

“They figured, surely to God we can move one person, surely we can badger and beat one person up,” he told Mr. Kercheval. “Surely we can get enough protesters to make that person uncomfortable enough that they’ll say, ‘Well, I’ll just vote for anything, just quit.’ Well, guess what? I’m from West Virginia.”

So what’s next?

Both Senator Chuck Schumer, the Senate majority leader, and Nancy Pelosi, the House speaker, offered a sunny outlook, saying that they didn’t believe negotiations with Mr. Manchin were over. The White House, despite an extraordinary statement on Sunday that effectively called Mr. Manchin a liar, didn’t pull the plug, either. “Senator Manchin and I are going to get something done,” Biden said Tuesday.

I asked Mr. Kott if there was any reason to believe that there could be a future for Build Back Better. His answer seemed to be one of education — both for Democrats trying to understand what Mr. Manchin wants and for Mr. Manchin himself, if he does hope to be the guy who can make a deal, and a big one at that.

“I don’t ever say anything is dead in Washington,” Mr. Kott said. “But when he says, ‘I can’t go home and I can’t explain this to West Virginia,’ that’s a serious line from him. He means that.”