Running for office involves a fair amount of political theatre, so it is no surprise that American presidential candidates often enlist the help of those who perform for a living.

In the current race for the White House, celebrity endorsements are stacking up much as you would expect in liberal Hollywood, where a large contingent of A-listers such as George Clooney, Lena Dunham and Jennifer Lopez are throwing their weight behind Democratic frontrunner Hillary Clinton.

The experts disagree on how significant such endorsements are, but if anyone needs to be convinced of the impact a major star can have, consider the US$353,400 (S$481,400) campaign contribution required for two seats at a table with Clinton, Clooney and the actor's wife Amal at a fund raiser in San Francisco last Friday.

Last night, the Clooneys were at it again, hosting a fund-raising dinner at their mansion here in Los Angeles, where tickets were going for US$33,400 a head.

In a letter to Clinton supporters inviting them to join a lottery for one of the tickets in exchange for a suggested donation of US$10, the 54-year-old star praised the former secretary of state as "the only grown-up in the room" and "the one consistent voice of tolerance and experience… who knows first-hand the complexity of our international relationships".

Other big names have also been stumping for the former first lady.

Dunham, the 29-year-old creator of the Golden Globe-winning HBO television series Girls, hit the campaign trail in several American cities earlier this year and documented her road trip in a travelogue posted on Clinton's website.

The actress and writer - who has a formidable social media presence and influential celebrity friends including pop star Taylor Swift - has not been shy about using press events for Girls to promote the candidate too.

Speaking to The Sunday Times at one such interview in Los Angeles, she says she is pro-Clinton because of the politician's stance on issues such as wage equality, reproductive justice and feminism, especially among women and younger voters.

"I admire what she does and if I can be useful in any way, like by going on the campaign trail for a few days, then I'm thrilled to do it," says Dunham, who even had her stylist put together special outfits so she could make a splash at these events.

"I wanted really patriotic, Hillarythemed stuff and it just made the whole thing more fun and playful because I was delivering pretty serious speeches about policy and human rights."

For Republicans in Hollywood, campaigning has been a rather more muted affair as conservatives have long been a minority in the left-leaning town.

Among those who veer right, the breeze seems to be blowing towards wildcard and frontrunner Donald Trump.

A conservative wealth manager with clients in the film and TV industry says most of them are Democrats. But he tells The Hollywood Reporter that for every Ted Cruz supporter he has spoken to, "there are 10 Trump supporters".

The magazine also reports that enthusiasm for Trump has been quietly growing in groups such as Friends of Abe, a secretive circle of politically conservative members of the Hollywood elite, whose roster includes actors Clint Eastwood, Jon Voight, Kelsey Grammer and Gary Sinise.

Yet many Trump backers are still in the closet. American Psycho author and screenwriter Bret Easton Ellis recently tweeted: "Just back from a dinner in West Hollywood: shocked the majority of the table was voting for Trump, but they would never admit it publicly."

Celebrities who have declared their allegiance to Trump seem to be mostly B- and C-listers, many with chequered histories of their own. They include pro-wrestler Hulk Hogan, boxer Mike Tyson, former basketball player Dennis Rodman and Scott Baio, star of 1970s sitcom Happy Days.

Like Trump, Democratic contender Bernie Sanders has painted himself as an anti-establishment candidate and, as such, has attracted a motley crew of celebrity backers.

Whereas Clinton has bagged most of the big names in Hollywood, the Vermont senator has been endorsed by the likes of actor Mark Ruffalo and Susan Sarandon, director Spike Lee, members of the Red Hot Chili Peppers and an assortment of minor rappers (50 Cent and Snoop Dogg are firmly in Team Clinton).

Backing a candidate is not a risk-free proposition for these performers, who put their reputations at stake when they hitch their wagons to a politician, especially a controversial and widely derided one such as Trump.

Supporting a respectable candidate such as Sanders or Clinton can come with a sting in the tail as well.

Thelma & Louise star Sarandon, 69, was roundly condemned by Democrats when she revealed that she would be reluctant to vote for Clinton should Sanders lose the nomination, arguing that a Trump presidency would be preferable because he "will bring the revolution immediately if he gets in".

Sanders, meanwhile, has used his rival's star-studded fund raising this weekend to hammer home his critique that she is too cosy with big-money donors - and, as one of them, Clooney found himself in the crossfire.

"I have a lot of respect for George Clooney - he's a great actor, I like him," Sanders told CNN. "But this is the problem with American politics… big money is dominating our political system. It is obscene that Secretary Clinton keeps going to big-money people to fund her campaign."

For a small fry like Baio, however, backing Trump has given his profile a little boost. The long-forgotten actor's name was briefly trending on Twitter the day he announced his endorsement.

A few Twitter users confessed that their first thought on seeing this was that Baio, 55, had died, or that there was going to be a remake of his Happy Days 1980s spin-off, Joanie Loves Chachi.

But as the saying goes, there is no such thing as bad publicity - especially in Hollywood.