WASHINGTON (AP) — President Joe Biden built his 2020 White House run around promises to beat Donald Trump "like a drum." As Biden gears up for an expected reelection campaign, he insists he can do it again.

But what if Trump isn't next year's Republican nominee?

Though the GOP primary race is only just beginning, a general election pitting Biden against any other Republican could look very different from one against Trump, with Democrats perhaps seeing enthusiasm to stop Trump at all cost evaporate.

Biden's continually low approval ratings and polling showing that many Americans — even a majority of Democrats — don't want him to seek a term that won't end until he's age 86 may also begin taking a bigger toll.

"I believe that, both for Biden and for Trump, going up against a new nominee would be more challenging than facing each other," said Julián Castro, a former Obama administration housing chief who ran against Biden in the 2020 Democratic primary.

For now, Trump remains a leading figure within the GOP and exercises tremendous influence among primary voters. Still, the field of Republican presidential candidates is beginning to expand with his former U.N. ambassador, Nikki Haley, announcing her candidacy. Polling suggests that GOP voters are open to backing someone other than Trump.

Beyond Haley, Florida Gov. Ron DeSantis could be a leading Trump alternative. More moderate challengers, such as former Maryland Gov. Larry Hogan, may soon emerge. Trump's vice president, Mike Pence, and secretary of state, Mike Pompeo, might run. South Carolina Sen. Tim Scott is planning to visit Iowa, fueling speculation about his political future.

All offer younger alternatives to both Biden and the 76-year-old Trump, and can promise fresher approaches to Washington, a point Haley made explicitly in her campaign kickoff. But so many choices could split the anti-Trump vote, perhaps allowing the former president to prevail in a fractured primary field.

Celina Vasquez, founder of the progressive group Texas Latinas List, said Biden's reelection appeal is built on his experience, not simply defeating Trump again.

"My generation, and the generation behind me, we've seen the dangers and the disaster of the MAGA Republicans," said Vasquez, whose organization promotes engagement by Texas Hispanic women at all levels of political office. MAGA is the acronym for the 2016 Trump campaign's slogan, "Make America Great Again," and has since become a general synonym for a descriptor of Trump policies and supporters.

Biden's political standing within his own party is perhaps stronger than it has ever been. After Democrats showed surprising resilience during last fall's elections, no major challenger has emerged to compete against the president in the party's upcoming primary.

Democrats also just replaced Iowa with South Carolina to lead off their 2024 primary at Biden's behest. And, despite still-high inflation, unemployment has fallen to its lowest level since 1969.

Top Democrats say another factor in Biden's favor is that, unlike former President Barack Obama, who was seen as a political phenomenon, Biden only got to the White House after two previous failed runs and was never viewed as a potentially transformational Washington force. That has kept the party and voters alike from falling into the complacency that contributed to Democratic losses in the 2010 and 2014 midterm elections under Obama.

For Biden, "the political nature of his presidency is one where Democrats around the country realize we all have a role to play in making sure he succeeds," said Ben Wikler, chair of the Wisconsin Democratic Party. "It's everybody's job."

Some voters in competitive states such as Georgia, however, say Democrats would be foolish not to think that a younger Republican nominee could capitalize on Biden's age.

"It really matters also who his actual opponent will be," Latabia Woodward, founder of Who's Got Next Music, a music tech platform in Atlanta, said after listening to Vice President Kamala Harris speak recently at Georgia Tech University. "But, as a strategy, I do believe that it is a concern and I think we need to prepare for it, not just react to it."

Doing so may not be easy. Polling from The Associated Press-NORC Center for Public Affairs Research shows that only 37% of Democrats say they want Biden to seek a second term — down from the 52% who backed the president running for reelection in the weeks before he led the party to a stronger-than-expected showing in November.

Among Republicans, 49% say they want Trump to run next year, while 50% do not. That's a modest shift from October, when 57% of Republicans reported wanting Trump to run.

Overall, just 22% of U.S. adults want Biden to run again compared to 27% who want Trump to run again.

Former House Speaker Paul Ryan, R-Wis., has said he thinks "anybody not named Trump" can beat Biden. Gov. Chris Sununu, R-N.H., himself mentioned as a possible White House 2024 contender, said Trump "can't get it done" against Biden.

Biden has shrugged off those findings, noting that he's been counted out before — for example, the recent midterms and when his 2020 campaign lost the first three Democratic primary contests in Iowa, New Hampshire and Nevada, only to be revived by a resounding South Carolina win.

Castro said beating Trump is a central argument for Biden's reelection, though equally important will be his legislative accomplishments, including a sweeping public works package, new gun safety rules and steep federal spending increases on green energy,high-tech manufacturing and health care. But Castro said polls nonetheless show an electorate not supportive of a second Biden term and that Democrats must "patch that up by the time he gets to the general election."

"Somebody can make the case out there – and right now there's nobody on the horizon – but there certainly seems to be an opening" for a Democratic primary challenger to Biden, Castro said, adding that it won't be him.

Biden's close aides acknowledge that, in 2020, he was laser-focused on having come out of retirement to deny Trump a second term. If Trump's not on next year's presidential general election ballot, they say, the president will broaden the contrasts he presents, seeking to make the race a referendum on broader Trumpism.

That's a strategy Biden effectively employed during the 2022 elections, when he constantly denounced "ultra-MAGA Republicans." He hinted there will be more where that came from, recently telling Univision that he didn't fear facing DeSantis more than Trump next year "because I think that they have a similar modus operandi, a similar way in which they work."

Biden allies say that the appeal of thwarting Trump can be expanded to Republicans as a whole because many in the party have either continued to embrace Trump's White House tenure or larger MAGA movement, or at least have struggled to condemn things such as spurious questioning of the 2020 election results and defending the mob that overran the Capitol on Jan. 6, 2021.

Many top Republicans also have, at one time or another, suggested they would support cuts to Medicare or Social Security, Biden aides note, a criticism the president has already begun lobbing.

The Democrats' midterm performance shows Biden was able to win last year without Trump on the ballot, and could do so again next year, those close to the president argue. Either way, they predict Biden will be buoyed in 2024 by two years of promoting trillions of dollars of reinvestment domestically.

That all resonates with Brandon Mayberry, an Emory University senior who also came to hear Harris in Atlanta. He said he plans to vote for Biden in 2024 regardless of who the president's opponent is, but admits that what happens next gives him pause.

"I like his passion as an 80-year-old man," Mayberry said. "But five, six more years –- that's kind of concerning."

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Associated Press writers Bill Barrow in Atlanta and Zeke Miller contributed to this report.