Barack Obama is reportedly preparing to endorse Hillary Clinton as early as this week, and will campaign aggressively to stop Donald Trump from succeeding him as president.
The president has so far remained on the periphery of the primary election contests, as Mrs Clinton has struggled to see off a challenge from Bernie Sanders and Mr Trump has claimed the Republican nomination. He has now indicated that he sees Mrs Clinton as the best guardian of his legacy, and will relish the opportunity to challenge Mr Trump more openly.
"I want us to run scared the whole time," he told a group of donors on Friday night, reflecting how seriously he is taking the election.
With his former secretary of state poised to clinch the Democratic nomination today, there are talks under way for how and when Mr Obama will officially make his endorsement, the New York Times reported. His intervention will provide Mrs Clinton with a much-needed boost.
Mrs Clinton, for her part, is also hoping a slew of celebrity endorsements will get her over the line in today's primary election in California.
Nearly all of Hollywood's leading men are backing the former secretary of state, including George Clooney, Tom Hanks, Leonardo DiCaprio and Ben Affleck. Eva Longoria has appeared at her rallies, while Morgan Freeman lends his unmistakable voice to one of her adverts. Beyonce and Katy Perry have chipped in, as have Kanye West and Kim Kardashian.
An election-eve concert last night was to be headlined by John Legend, Stevie Wonder and Christina Aguilera.
Mr Sanders, Mrs Clinton's dogged rival, can also count several celebrities among his supporters, but they are a less glamorous bunch. Where Mrs Clinton has Robert De Niro, he has Danny DeVito. While he has Spike Lee, she has Steven Spielberg.
But it is Mr Sanders who has been drawing massive crowds at his rallies in California in the weeks leading up to today's election. Supporters waited more than five hours to see him speak in Irvine last month, and thousands were expected at a rally last night in San Francisco. The Vermont senator has even managed to use Mrs Clinton's celebrity support against her, describing a pounds 23,000-per-plate fundraiser held at Clooney's home in April as a manifestation of "the problem with American politics".
"I have a lot of respect for George Clooney," Mr Sanders said. "He's a great actor. I like him. But this is the problem with American politics ... Big money is dominating our political system."