Concerns about the president’s age are being overcome by enthusiasm about his record so far, optimism about the G.O.P. field — and the absence of better options.PHILADELPHIA — Nine months ago, amid sky-high gas prices and legislative gridlock, anxious Democrats routinely offered the same assessments of President Biden as a candidate for re-election: too frail, too politically weak, too much of a throwback.But now, as Democratic National Committee members gather in Philadelphia for their winter meeting this week, nearly all have come to the same conclusion: It’s Biden or bust.After Democrats far exceeded their own expectations in the midterms, and now that they are facing the possibility of a rematch against a far more vulnerable Donald Trump, the bickering about Mr. Biden has subsided.With no other serious contenders making early moves to enter the race, the official party structure has united behind the president’s re-election bid — despite the inherent risks in an octogenarian candidate’s undertaking the rigors of a national campaign.Gov. Phil Murphy of New Jersey, who is chairman of the Democratic Governors Association, an organization full of members predisposed to imagine themselves in the White House, said any discussion of possible challenges had gone quiet in recent months.“I don’t hear any chatter of anybody considering taking him on in our party, and I think for good reason,” Mr. Murphy said. “What I see is a guy who’s still on top of his game.”While challenges to a sitting president are rare, the lack of even a whisper of intraparty opposition this year is notable given Mr. Biden’s already record-setting age as president. If he won, he would be 82 when sworn in for a second term.Mr. Biden greeted Avery Tierney, 9, of Marlton, N.J., at the D.N.C. gathering.Al Drago for The New York TimesIn Philadelphia, where delegates chanted “four more years” as Mr. Biden spoke on Friday evening, concerns about his age were confined to quiet conversations — a tacit recognition that the time had passed for Democrats to question the wisdom of nominating a member of the Silent Generation. Despite months of speculation about a restive bench of potential challengers, no serious Democratic contenders appear to be doing the kinds of donor outreach, staff hiring or visits to early-primary states that typically portend a presidential bid.Nor is there any clamoring for a primary race — to hedge Democratic bets or to ensure Mr. Biden addresses any perceived vulnerabilities well before a general election — even amid an expanding investigation into Mr. Biden’s mishandling of classified documents.The Democrats’ Primary CalendarA plan spearheaded by President Biden could lead to a major overhaul of the party’s presidential primary process in 2024.Demoting Iowa: Democrats are moving to reorder the primaries by making South Carolina — instead of Iowa — the first nominating state, followed by Nevada and New Hampshire, Georgia and then Michigan.A New Chessboard: President Biden’s push to abandon Iowa for younger, racially diverse states is likely to reward candidates who connect with the party’s most loyal voters.Obstacles to the Plan: Reshuffling the early-state order could run into logistical issues, especially in Georgia and New Hampshire.An Existential Crisis: Iowa’s likely dethronement has inspired a rush of wistful memories and soul-searching among Democrats there.“Let me ask you a simple question: Are you with me?” Mr. Biden asked the crowd of D.N.C. members on Friday night, to boisterous cheers. An even more overt acknowledgment is to be made on Saturday, when Democrats are set to vote on a measure that would make it vastly more difficult for a potential primary challenger to catch fire. A new primary calendar, devised by Mr. Biden and his advisers, would vault to the front a number of states that propelled him to the nomination in 2020, starting with South Carolina.Still, with the election 641 days away, much remains uncertain. The shape of the Republican field remains unclear, as does the country’s economic forecast. And while Mr. Biden intends to run for re-election, he is unlikely to announce his campaign until the early spring, according to people close to the president, and is still working through key details like hiring a campaign manager. (Were Mr. Biden not to run, Vice President Kamala Harris could benefit from the new calendar, which increases the influence of states where Black voters make up a large portion of the primary electorate.)Gov. Phil Murphy of New Jersey, the chairman of the Democratic Governors Association, said chatter about possible primary challengers to Mr. Biden had gone quiet.Bryan Anselm for The New York TimesMany Democrats feel warmly about Mr. Biden, a party stalwart for half a century, and are hesitant to appear disloyal or insensitive by publicly questioning his fitness for a second term. They are also keenly aware of how primary challenges weakened incumbent presidents: Several Biden allies pointedly mentioned Senator Edward M. Kennedy’s failed 1980 primary race against President Jimmy Carter, who then was defeated by Ronald Reagan..css-1v2n82w{max-width:600px;width:calc(100% – 40px);margin-top:20px;margin-bottom:25px;height:auto;margin-left:auto;margin-right:auto;font-family:nyt-franklin;color:var(–color-content-secondary,#363636);}@media only screen and (max-width:480px){.css-1v2n82w{margin-left:20px;margin-right:20px;}}@media only screen and (min-width:1024px){.css-1v2n82w{width:600px;}}.css-161d8zr{width:40px;margin-bottom:18px;text-align:left;margin-left:0;color:var(–color-content-primary,#121212);border:1px solid var(–color-content-primary,#121212);}@media only screen and (max-width:480px){.css-161d8zr{width:30px;margin-bottom:15px;}}.css-tjtq43{line-height:25px;}@media only screen and (max-width:480px){.css-tjtq43{line-height:24px;}}.css-x1k33h{font-family:nyt-cheltenham;font-size:19px;font-weight:700;line-height:25px;}.css-1hvpcve{font-size:17px;font-weight:300;line-height:25px;}.css-1hvpcve em{font-style:italic;}.css-1hvpcve strong{font-weight:bold;}.css-1hvpcve a{font-weight:500;color:var(–color-content-secondary,#363636);}.css-1c013uz{margin-top:18px;margin-bottom:22px;}@media only screen and (max-width:480px){.css-1c013uz{font-size:14px;margin-top:15px;margin-bottom:20px;}}.css-1c013uz a{color:var(–color-signal-editorial,#326891);-webkit-text-decoration:underline;text-decoration:underline;font-weight:500;font-size:16px;}@media only screen and (max-width:480px){.css-1c013uz a{font-size:13px;}}.css-1c013uz a:hover{-webkit-text-decoration:none;text-decoration:none;}How Times reporters cover politics. We rely on our journalists to be independent observers. So while Times staff members may vote, they are not allowed to endorse or campaign for candidates or political causes. This includes participating in marches or rallies in support of a movement or giving money to, or raising money for, any political candidate or election cause.Learn more about our process.Indeed, Mr. Biden’s age is one reason many Democrats are hoping that Mr. Trump, who at 76 is just four years younger, wins the G.O.P. nomination. After years of worrying about Mr. Trump’s political potency, many Democrats scarred from underestimating him in 2016 now see him as eminently beatable, especially by Mr. Biden.But some fear that a contest between Mr. Biden and a younger challenger, like Gov. Ron DeSantis of Florida or former Gov. Nikki Haley of South Carolina, could create a more challenging contrast for the president.“Trump would be a preferred candidate,” said Jay Jacobs, chairman of the New York State Democratic Committee, even as he said he believed Mr. Biden would be strong regardless and noted that Mr. DeSantis was untested on the national stage. But a younger nominee, he added, “mixes it up in a way that you don’t have any ability to judge how it will look going forward.”At a moment when Democrats regard the return of Mr. Trump, or the rise of someone practicing his style of politics, as a threat to democracy, there is enormous pressure from all corners of the party to avoid damaging Mr. Biden.“Speaking as a progressive, Biden was not my first choice for president, but I think he’s done an extremely good job with the hand that he’s been dealt,” said RL Miller, a climate activist and Democratic National Committee member from California. “I find the talk of 2024 challengers to him to be both disrespectful and distracting.”But elections are determined by voters, not party officials, and the Democratic base has concerns about another Biden bid, even if the party’s officials see the president as their strongest option. Majorities of Democrats in surveys conducted in December, a month after the party’s unexpected midterm successes, said they did not want Mr. Biden to seek re-election.“The majority of the party and Biden voters didn’t vote for Biden, they voted against Trump,” said Liano Sharon, a delegate from Michigan who voted for Biden in 2020. “If the party pushes Biden on the grass roots again, a lot of them aren’t going to show up, because of Biden’s policies, broken promises and other big problems,” including his concern that Mr. Biden was showing signs of decline.That view had little support in Philadelphia, however, where the only sign of opposition to a Biden re-election bid was a billboard on the back of a truck circling outside, advertising a group calling itself DontRunJoe.org. Its founder, Jeff Cohen, conceded as much: “We’re beating our heads against the wall here,” he said.Without a viable alternative willing to jump into the race, elected Democrats and top party officials find themselves like the dinner party guests in a horror-film spoof on “Saturday Night Live” last year who are terrified of a 2024 Biden candidacy but even more scared of the other possible candidates. Several Democratic officials brought up the sketch unprompted to describe their attachment to a Biden re-election bid.“What is the alternative? Like, who’s the alternative?” said Representative Ritchie Torres of New York, casting Mr. Biden as a strong contender with “the most consequential presidency in recent history.” He added, “If I’m asked who is best positioned to win in 2024, I’m unaware of an alternative to President Biden.”After Gov. J.B. Pritzker of Illinois pledged allegiance to Mr. Biden, other big-name Democrats seen as White House material followed suit.Michelle Litvin for The New York TimesSo far, no prominent Democrats are taking even cursory steps to establish themselves as presidential timber. Gov. J.B. Pritzker of Illinois made a much-remarked-upon trip to New Hampshire last summer, but he has pledged allegiance to Mr. Biden. Other big names, including Gov. Gavin Newsom of California and Gov. Gretchen Whitmer of Michigan, have followed suit.Only Marianne Williamson, the self-help author who ran a quixotic presidential campaign in 2020, has acknowledged mulling a primary challenge, citing concerns over a Democratic Party that she said had “swerved from its unequivocal and unabashed advocacy for the working people.”In an interview, Ms. Williamson said she would not run “simply to make a point” but to give Americans options. “The question I ask myself is not ‘What is my path to victory?’” she said. “My question is ‘What is my path to radical truth-telling?’ There are some things that need to be said in this country.”Absent more credible potential primary threats, Biden allies are reveling in a sense of vindication after a stressful midterm campaign. Mr. Biden, they say, will counter concerns about his age in his re-election campaign with arguments about the value of his long experience in government.“He’s always underestimated by people in his party and outside his party,” said former Representative Cedric L. Richmond, who served as a senior adviser to Mr. Biden at the White House, rattling off a list of the president’s legislative accomplishments. “They said he couldn’t win the presidency. He did.”But the next election may bear little resemblance to the last. Unlike in 2020, when Mr. Biden conducted much of his campaign over video from his basement because of the coronavirus, his re-election bid could require the kind of grueling travel that has long been customary in presidential contests. A noticeably more languid pace by Mr. Biden could set up a stark contrast if Republicans abandon Mr. Trump in favor of a younger nominee.Bill Shaheen, a D.N.C. member from New Hampshire, called Mr. Biden “physically fit” and energetic.But, drawing on personal experience, Mr. Shaheen, who is 79, added, “There’s only so much you can do when you’re our age.”Having helped run primary campaigns in New Hampshire for presidents as far back as Mr. Carter and campaigned for his wife, Senator Jeanne Shaheen, Mr. Shaheen said they could be exhausting. “By the time the primaries were done, I was wiped out,” he said. “And the general election, as well — I mean, it is extremely physically demanding.”Still, Mr. Shaheen, who has strongly disagreed with Mr. Biden’s effort to reshuffle the presidential primary calendar — a move that would make New Hampshire the second contest alongside Nevada, rather than the first primary — said that if Mr. Biden wants to run again, “I want him to do it.”Kitty Bennett contributed research. 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