President Joe Biden has begun a three-day, star-studded fundraising trip in California by mocking Republican frontrunner Donald Trump for claiming he would be a dictator just on his first day in office if he becomes president again.

Trump said on Tuesday he would not become a dictator if he became US president again, except “on day one”.

“Thank God, only one day,” Biden quipped at a fundraiser in Los Angeles at the home of celebrity interior designer Michael Smith and his partner, James Costos, a former HBO executive who was President Barack Obama’s ambassador to Spain.

The second order would be drill for oil and gas to lower prices at the pump.

Biden, by contrast, signed 17 executive orders within hours of his inauguration, including one that stopped the construction of Trump’s southern border and others that restricted drilling.

Biden called Trump, who lost the 2020 election but sought to challenge the results, “a threat to democracy”.

Problem child

Trump was indicted in August for wide-ranging attempts to overturn the election.

Biden’s trip comes a day after the Department of Justice filed new criminal charges against his son Hunter, accusing him of failing to pay $US1.4 million ($A2.1 million) in taxes while spending millions of dollars on drugs, prostitutes, designer clothes and cars.

Biden made no mention of his son during his remarks at the fundraiser.

California – and its deep-pocketed entertainment industry – has long served as a major funding source for Democrats, but long strikes by actors and screenwriters have had a chilling effect on fundraising.

The end of the labour unrest has unlocked pent-up dollars, said Jeffrey Katzenberg, a movie mogul and campaign co-chair who has emerged as an influential voice in Biden’s effort to win re-election in November 2024.

“It will be the most successful day and a half for the campaign to date and likely one of the most successful days and a half prior to a general election, where things sort of kick into a whole other gear, that we’ve ever had out here for any candidate ever,” Katzenberg said in an interview with Reuters.

Biden was scheduled to participate in two Los Angeles fundraisers expected to include directors Steven Spielberg and Rob Reiner and musicians Barbra Streisand and Lenny Kravitz.

The California swing is part of a blitz of at least nine fundraisers Biden will hold before the end of the month.

-AAP