“If Biden is elected,” a prominent adviser to the campaign said, “he’s going to be 82 years old in four years and he won’t be running for reelection.”

The adviser argued that public acknowledgment of that reality could help Biden assuage younger voters, especially on the left, who are unexcited by his candidacy and fear that his nomination would serve as an eight-year roadblock to the next generation of Democrats.

By signaling that he will serve just one term and choosing a running mate and Cabinet that is young and diverse, Biden could offer himself to the Democratic primary electorate as the candidate best suited to defeat Trump as well as the candidate who can usher into power the party’s fresh faces.

“This makes Biden a good transition figure,” the adviser said. “I'd love to have an election this year for the next generation of leaders, but if I have to wait four years [in order to] to get rid of Trump, I'm willing to do it.”

Another top Biden adviser put it this way: “He’s going into this thinking, ‘I want to find a running mate I can turn things over to after four years but if that’s not possible or doesn’t happen then I’ll run for re-election.’ But he’s not going to publicly make a one term pledge.”

In elite Democratic circles, conversations about Biden’s age and whether to address it with a one-term pledge have become more urgent in recent weeks as Biden has solidified his once shaky standing in the Democratic primaries.

Since Thanksgiving there has been a gradual shift among prominent Democrats once deeply skeptical of Biden’s candidacy. In national polls, Elizabeth Warren, who was on a trajectory to topple Biden, has lost all the gains she achieved since July and fallen to third place. Pete Buttigieg, who has replaced Warren as the hot candidate among white college-educated voters, has shown no evidence that, even as he thrills a subset of the Democratic electorate in Iowa, he can achieve broad appeal among African American and Latino voters. Meanwhile, Sen. Bernie Sanders, who won 43 percent of the primary vote in 2016, has been unable to break out of the mid-teens for most of this year.

Biden’s base of older working-class white and African American voters has been unassailable. A year of national polling of the Democratic primary shows his remarkably consistent support. According to the Real Clear Politics national polling average on Dec. 8, 2018, Biden had 29 percent support nationally. On Dec. 8, 2019, he had 29 percent support.

The greatest threats to Biden’s African-American base have been neutralized. Sen. Kamala Harris has suspended her campaign. Sen. Cory Booker has struggled to qualify for the PBS News Hour/POLITICO Debate, on Dec. 19. Former Gov. Deval Patrick, a pre-Thanksgiving entrant to the race, has barely been heard from and is polling at less than 1 percent.

This current bright spot could just be some momentary sunshine for Biden before storm clouds gather. Biden’s position in Iowa and New Hampshire, overwhelmingly white states packed with college-educated Democrats unexcited by his candidacy, is middling. Poor showings in both states could upend the race. Warren, who has built a robust national campaign and is generally seen by Biden’s advisers as the strongest primary opponent remaining, could still make a comeback. Biden has struggled with fundraising, while all three of his top opponents — Warren, Sanders, and Buttigieg — have demonstrated the potential to fund a long campaign against him. Mike Bloomberg, the billionaire who has quietly bought himself into fifth place by spending tens of millions of dollars on television ads, looms as a potential Super Tuesday threat on March 3, after the first four states have voted.

But, for now, Biden remains the favorite, a fact that even the online betting markets, which were wildly bullish on Warren from September through November, now acknowledge.

And so the question of how to address Biden’s age, which may be the candidate’s most significant liability, and the related question of the lack of enthusiasm for Biden’s candidacy among the activist wing of their party, has once again seized Democrats.

A top Biden adviser said that Biden ruled out a one-term pledge when the issue was raised before he even entered the race. “He said it was a nonstarter,” the adviser said, adding that Biden believed it was a “gimmick.”

But Biden’s public statements on running for reelection have shifted over the course of the campaign.

In April, when asked if he would serve just one term, Biden responded, “No.” More recently, Biden has been ambiguous. In October, the Associated Press reported that when “asked whether he would pledge to only serve one term if elected, Biden said he wouldn’t make such a promise but noted he wasn’t necessarily committed to seeking a second term if elected in 2020.”

“I feel good and all I can say is, watch me, you’ll see,” he told the AP. “It doesn’t mean I would run a second term. I’m not going to make that judgment at this moment.”

Kate Bedingfield, Biden’s deputy campaign manager and communications director, declined to comment when asked whether Biden had ruled out running for reelection if he wins the Democratic nomination and defeats Trump.

Several advisers downplayed the idea of a formal pledge. Others emphasized that there were better ways to address concerns about Biden’s age, such as by using his age as a proxy for experience. (Biden recently challenged a voter to an IQ test or push-up competition.) But the issue remains a topic of debate inside and outside the campaign, and several advisers now quietly acknowledge that while Biden won’t run for reelection he cannot say so publicly.

But the case for going public has some advocates.

A political strategist who has recently talked to one of Biden’s closest advisers made the argument for serving one term this way: “Is 81 years old too old to be president? Yes. Is an eighty-one year-old president standing for reelection likely to be successful? He is not. And is it the right thing to do for the country? No. Biden wouldn’t be running if it were President Jeb Bush or President Marco Rubio. He’s running because it’s an exigent circumstance — Donald Trump. The next president will have to have oppositional virtues to the last president. We have a presidency that is defined by abject selfishness, self-regard and self-interest. So a one-term pledge would be viewed as an act of selflessness, putting the country ahead of any ambition.”

One adviser to Biden who favors a one-term pledge argued that if he wins and his presidency is a success and he’s healthy enough to run for reelection he could always reverse the pledge if Democrats wanted him to remain their candidate in 2024.

But many prominent Democrats believe a public pledge to serve only one term would do more harm than good, a conclusion also reached by Republican advisers to John McCain in 2008, when the then-72-year-old GOP nominee considered making such a commitment.

“That’s a weak play,” said John Podesta, Hillary Clinton’s 2016 campaign chairman. “I think who his vice president is will be very important because people will be thinking about that. But I don’t think I would make a one-term pledge. You’ve disempowered yourself as president and I don’t think it helps you as a candidate. It accentuates your weakness. It doesn’t fix it.”

That’s why the campaign’s current course of strategic ambiguity may be the best approach for Biden right now, key advisers believe. It keeps the issue alive without ruling out a more formal pledge later on. If Biden’s fortunes decline and the pledge makes more political sense it can always be revived. Alternatively, if being seen as a one-termer weakens him in the primary or general election, he can say unequivocally that he will seek reelection.

“I think he should make [the one-term pledge] privately to himself and his wife and no one else,” said one well-known Democratic strategist. “You can’t let the cat out of the bag. Go back to that old Jimmy Breslin essay on power — you know it's a lot of smoke and mirrors. If you begin your first day as president as a lame duck, it changes everything. Every Cabinet secretary, every subcommittee chairman treats you differently. I wouldn’t advise it just from a governing perspective as well as political.”

He added, “But I would actually do it because it’s crazy for him to run for a second term. It’s a bit crazy to run for a first.”

Natasha Korecki contributed to this report.