Senator Joe Manchin III, the conservative West Virginia Democrat, was attending an event in his home state last month when he made a joke that quickly touched off the latest round of feverish speculation about his political future.
“I will also endorse Jim for basketball coach,” Mr. Manchin said, suggesting that the popular Republican governor, Jim Justice, who has announced he will seek Mr. Manchin’s Senate seat next year, should instead be hired by West Virginia University to pursue his lifelong passion on the court.
The comment seemed to suggest that Mr. Manchin, who has flirted with bolting his party and running for president as an independent, had not given up on defending his Senate seat.
But as the last pivotal Democratic senator who has not yet said whether he will seek re-election, Mr. Manchin still has Washington and his party guessing about his plans.
Behind closed doors, Senator Chuck Schumer of New York, the majority leader, has been relentlessly encouraging him to run, regarding Mr. Manchin — perhaps the only Democrat with a chance to win a statewide contest in deeply conservative West Virginia — as key to preserving his party’s tenuous control of the Senate. Democrats across the country have been praying that he will seek re-election rather than pursuing a presidential bid through the centrist political group No Labels, which could draw votes from President Biden and help elect a Republican.
For a man who routinely seeks the spotlight when faced with politically consequential decisions, this is among the most closely watched dilemmas Mr. Manchin has confronted.
“I don’t have a clue what he’s going to do, and I don’t think he knows what he’s going to do,” said Phil Smith, the longtime chief lobbyist for the United Mine Workers of America and a close ally of Mr. Manchin’s.
In a brief interview in the basement of the Senate this week, Mr. Manchin said he would make a decision about his future by the end of the year. If he intends to run for re-election, he must inform the state by January.
“The bottom line is, I’ve been in West Virginia for a long time and moving in the right direction,” he said. “Our approval rating’s up quite substantially in a very, very, very red state. So I feel very good about all those things.”
He added, “We’ve got plenty of time.”
Still, decisions will have to be made before the political terrain becomes completely clear. The most important of his considerations is which Republican he would face. To win the nomination, Mr. Justice, a wealthy Democrat turned Republican, would have to defeat Representative Alex X. Mooney, a more reliable ally of former President Donald J. Trump’s.
A poll last week for the West Virginia Chamber of Commerce encapsulated Mr. Manchin’s conundrum. The senator and the governor are both popular in the state, with 56 percent of voters approving of the job Mr. Justice has done and 51 percent approving of Mr. Manchin’s performance, numbers above even Mr. Trump’s 49 percent approval rating.
While the poll showed Mr. Justice beating Mr. Manchin handily in a hypothetical Senate contest, 51 percent to 38 percent, the poll also found that Mr. Manchin would narrowly lead Mr. Mooney, 45 percent to 41 percent.
(Mr. Manchin’s allies point out that his approval rating increased by 9 percentage points since 2021 in the poll, while Mr. Justice declined by 5 points.)
The conservative political action committee Club for Growth has said it will back Mr. Mooney in the primary. Joe Kildea, a spokesman for the group, said its political arm had raised about $14 million and would spend “whatever it takes.” That could bloody Mr. Justice, but money alone may not be enough for Mr. Mooney, who trails the governor among West Virginia Republican voters, 58 percent to 26 percent.
“We beat big-government, establishment RINOs all the time,” said David McIntosh, the president of Club for Growth, referring to the conservative slur “Republicans in name only.”
It is also unclear whether Mr. Trump will seek to get involved in the primary, set for May 14. In 2022, he endorsed Mr. Mooney in a House Republican primary against Representative David B. McKinley, and Mr. Mooney won easily. This time around, Mr. Trump is extremely unhappy with Club for Growth, which has funded an advertising campaign in Iowa imploring Republicans to back a different presidential candidate. Then again, he also likes to counter Senator Mitch McConnell of Kentucky, the minority leader, who backs Mr. Justice.
Mr. Manchin’s allies claim that none of that is weighing particularly heavily on the senator these days.
“I know it’s shocking in D.C., but Joe Manchin isn’t focused on partisan politics this year,” said Jonathan Kott, his former senior adviser in the Senate. “He will sit down with his family at the end of the year and figure out how he can best serve the people of West Virginia and the country.”
Yet the timeline set by No Labels for a possible independent presidential run has complicated Mr. Manchin’s calculations. So far, the group has qualified for a spot on the presidential ballot in only 11 states and is hustling to make the ballot in many more. And though No Labels leaders still insist they will only start a “unity” ticket for the White House if the major party nominees do not move to the political center, the group has set a date in April for a convention in Dallas to choose its candidates.
That means Mr. Manchin would be choosing between the Senate run and a White House bid before he knew whether No Labels would select him.
His third option might be simply to retire at 76. His alma mater, West Virginia University, is in deep trouble, slashing its budget, laying off faculty and even eliminating its foreign language program. Its president, E. Gordon Gee, turns 80 in February, and a chance to lead the university out of crisis would be tempting for the senator, Mr. Manchin’s allies said.
One official with close ties to the senator pointed to the decision of one of his former chiefs of staff, Larry Puccio, to sign on with Mr. Justice as an indication that Mr. Manchin will retire.
Adding to the intrigue, the senator’s daughter Heather Manchin has started a nonprofit organization, reported earlier by The Wall Street Journal, that is trying to raise more than $100 million to promote centrist policies. Those familiar with the organization, which is currently independent from Mr. Manchin, said it could serve as a landing pad for the senator if he retires from politics. The group could also conduct market research on policies and messaging that would prove useful to his presidential aspirations should he run, though Ms. Manchin denied that had anything to do with it.
“This movement is not about starting a third party or rallying behind any one individual,” she said.
The No Labels flirtation has perplexed some of Mr. Manchin’s allies and some political observers. Senate aides say Mr. Manchin is seriously considering it, but others suggest that he is simply using the prospect of a third-party presidential run to keep his name in the news, pressure Mr. Biden to address his policy priorities as he carries out the Inflation Reduction Act and raise money for whatever he decides to do next.
A possible rival for the No Labels ticket has already emerged in Larry Hogan, a moderate Republican and the former governor of Maryland.
Mr. Hogan, appearing on CBS’s “Face The Nation” on Sunday, implied that the name at the top of the No Labels ticket would have to be a Republican to ensure that the independent campaign would take at least as many votes from the current Republican front-runner, Mr. Trump, as from Mr. Biden. Democrats, he said, should relax.
Mr. Manchin’s possible candidacy “is really what set them off in a panic,” Mr. Hogan said.
It was at an event in Beckley, W.Va., for former Representative Nick Rahall, one of the last Democrats to represent the state in Congress, that Mr. Manchin made the quip about West Virginia University hiring Mr. Justice to coach basketball, after Mr. Gee had suggested it.
The event was a dedication of Mr. Rahall’s archives, and the crowd was full of former Democrats, including Mr. Justice. Mr. Manchin was the last of his kind.
Still, Mr. Rahall left confident in the senator’s survival.
“Joe Manchin has said if he enters the race, he will win, and I believe him when he says that,” Mr. Rahall said. “Now, he hasn’t said which race he’ll enter.”
