President Joe Biden has made his first trip to California on the eve of a rare state recall election to shore up support for Governor Gavin Newsom.
Polls show a comfortable lead for the Democrat, whose main rival, Larry Elder, is a conservative radio host.
It is only the second-ever recall for a governor to appear on the ballots of the Democratic state.
Mr Biden and Mr Newsom are expected to hold a rally together later on Monday.
Since he took office in 2019, Gavin Newsom has cemented California’s status as America’s progressive and free-spending state.
But frustration over his handling of the pandemic and increasing partisanship in US politics has fuelled a Republican-led effort to supplant him before his term ends.
He is now facing some 46 candidates, including transgender activist and reality TV star Caitlyn Jenner.
California has been firmly Democratic in national elections, but the state does have Republican regions – and six million voters there cast ballots for Donald Trump in 2020.
High enthusiasm among this voting group has raised tensions ahead of Tuesday’s election. Mr Biden is now one of several high-profile Democrats to campaign on behalf of Mr Newsom – Vice-President Kamala Harris visited the state last week.
The last successful recall election of a California governor, in 2003, led to Arnold Schwarzenegger taking over the role. There have been consistent attempts to call such elections against Golden State governors since the late 1960s.
Leading opponent Mr Elder spent the day campaigning in Los Angeles and Orange counties. He has never previously held political office and received a boost of support over the weekend from actress Rose McGowan.
In a news conference, McGowan claimed that Mr Newsom’s wife, Jennifer Siebel Newsom, had offered her a bribe to bury her accusation of rape against Hollywood film mogul Harvey Weinstein.
Mrs Newsom’s team has called the allegations “a complete fabrication”, the Los Angeles Times reported.
In the final days of the race, state Republicans have been casting false claims of election rigging.
The move harkens back to Mr Trump’s discredited claims of voter fraud in the 2020 presidential election. On Monday, Mr Trump described the recall vote as “rigged”.
In an interview with NBC on Monday, Mr Elder declined to say whether he would accept the results of the election.