Los Angeles, California - President Joe Biden brushed aside the jet lag Saturday, flying straight from the G7 in Italy to Los Angeles to a star-studded fundraiser set to bring millions of dollars for his election fight against Donald Trump in November.

Hollywood stars George Clooney and Julia Roberts will join former president Barack Obama for the gala evening that Biden's campaign says has already raised $28 million – the most in Democratic party history.

But his turn with the stars means Biden is skipping a huge international peace conference for Ukraine in Switzerland on Saturday, with Vice President Kamala Harris attending instead.

Biden's campaign said the fundraiser was a "show of force with leaders across the entertainment industry sending a clear signal: they are united and enthusiastic about re-electing President Biden and Vice President Harris."

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The glitzy fundraiser will be a brief change for 81-year-old Biden after a recent run of grueling foreign travel, and geopolitics focused on the grinding conflicts in Ukraine and Gaza.

At the Group of Seven rich nations summit in Puglia, Biden helped seal a deal for a $50 billion loan for Ukraine using frozen Russian assets and signed a 10-year security accord with President Volodymyr Zelensky.

The week before, he was in Normandy, France, for the 80th anniversary of the World War II D-Day landings.

In Los Angeles, Biden and Obama, under whom he served as vice president, will take part in a conversation moderated by late-night comic Jimmy Kimmel.

Actors Clooney and Roberts, Jack Black, and Justin Bateman will also take part in the event in the city's Peacock Theatre, which will reportedly end with a surprise musical guest.

Biden's switch from geopolitics to US electioneering also marks the start of a new and more intense phase in his battle with Trump ahead of November's knife-edge election.

Trump will visit a Black church in Detroit on Saturday as he attempts to woo a group of voters whose support for Biden recently appears to have ebbed, despite Trump's history of questionable comments on racial issues.

Polls show that Biden and Trump are largely neck-and-neck, with many voters turned off by a rematch between the oldest president in US history and a 78-year-old convicted felon.

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They have been in a fundraising battle too, with Biden raking in more for months but Trump doing better recently as supporters rally over the guilty verdict in his porn star hush money trial.

Biden's campaign said the $28 million from the LA fundraiser would help staff and build offices in battleground states and buy broadcast advertising.

The two are also gearing up for the first blockbuster debate of the presidential campaign in less than two weeks. Biden is expected to head to the presidential Camp David retreat next week to start preparing for the June 27 debate.

The Democrat is expected to go on the offensive on issues like abortion and democracy, where his campaign thinks Trump is vulnerable. But he will also be preparing for how to deal with full-frontal personal attacks by the former reality TV show host.

For the CNN debate in Atlanta later this month, microphones will be muted except when it is their turn to speak.