Voters say neither Biden nor Trump should run in 2024 - Reuters/Ipsos

About half of US Democrats say President Joe Biden should not seek re-election next year and that he is too old to run, a worrisome sign for the 80-year-old, a Reuters/Ipsos poll found.

The three-day opinion poll completed on Monday, a day before he announced his re-election bid, showed an American public unenthused by the prospect of a rematch between Biden and his predecessor and current leading Republican rival, Donald Trump, with about two-thirds of respondents overall not wanting either to run again in 2024.

Among their own parties, 44% of registered Democratic respondents said Biden should not seek a second term, compared to 34% of Republicans who said Trump should not run again, according to the national poll.

Since taking office in January 2021, Biden has been dogged by high inflation and low approval ratings. Just 41% of poll respondents – including 74% of Democrats and 10% of Republicans – approved of his performance as president.

His re-election campaign faces the challenge of sparking enthusiasm among Democrats to ensure they come out to vote in November 2024.

Biden is expected to face scant opposition in Democratic presidential nomination contests after he was credited with helping the party do better than expected in the 2022 congressional elections. Democrats lost control of the House of Representatives but retained a Senate majority, thanks in part to voters fired up by the Supreme Court decision ending the national right to abortion.

Biden is the oldest person to have occupied the White House and would be 86 at the end of a second four-year term. Sixty-one percent of registered Democrats in the poll said he was too old to work in government.

By comparison, only 35% of registered Republicans said Trump, 76, was too old.

Biden beat Trump in 2020 by winning the Electoral College 306 to 232. He won the swing states of Pennsylvania and Georgia, and he bested Trump by more than 7 million votes nationally, capturing 51.3% of the popular vote to the Republican's 46.8%.

Trump is the frontrunner for the Republican nomination and was the pick of 50% of registered Republicans in the poll, trailed by Florida Governor Ron DeSantis, who was favoured by 24% of the party though he has not yet declared his candidacy.

In a hypothetical one-on-one contest, Biden led Trump 43% to 38% among registered voters, a lead for the Democrat that was just outside the poll's 4 percentage point credibility interval for registered voters. Biden also led among independent voters.

In another hypothetical two-person match up, DeSantis trailed further behind, with 34% to Biden's 43%.

The Reuters/Ipsos poll gathered responses from 1,005 adults across the United States, including 445 self-described Democrats and 361 Republicans.