President Obama's got Beyonce, Honey Boo Boo and George Clooney on his side. Republican Mitt Romney has Donald Trump, Donny and Marie Osmond, and Chuck Norris rooting for him.

Each of the presidential contenders has a catalog of celebrity endorsements about which he boasts, from A-listers like Clooney to lesser-knowns like Scott Baio (of TV's "Happy Days"), who backs Romney. Rocker Bruce Springsteen is singing Obama's praises. Romney has Kid Rock.

And each has to contend with the handful of endorsements that the candidates probably wish the celebrities had kept to themselves, like reality TV personality Honey Boo Boo, an Obama backer, and troubled starlet Lindsay Lohan, a Romney supporter.

A nod from someone in Tinseltown doesn't really influence voters one way or the other, experts say. But stars definitely can fatten campaign coffers, particularly for Democrats.

The ultimate test of celebrity influence came in 2007, when TV host Oprah Winfrey announced her support for Obama, helping to pack his campaign rallies.

Oprah's backing was credited at the time with helping Obama defeat Hillary Clinton in the 2008 Democratic primary and, ultimately, with helping him defeat Republican John McCain in the general election.

A study by two University of Wisconsin-Milwaukee professors, however, determined that Oprah got more credit than she deserved.

Oprah's endorsement "did not influence the extent to which [study] participants held favorable opinions toward Obama or the extent to which they saw him as likable," professors Andrew Pease and Paul Brewer concluded.

Oprah's influence may have been "overhyped," Brewer said. But that's not to say Oprah had no effect. She did raise a create a sense of viability for Obama in voters' minds, helping them see him as potential winner.

"It influenced whether people thought Obama had a good chance of winning," Brewer, now at the University of Delaware, told The Washington Examiner.

So will Beyonce and Clooney give Obama an advantage this year?

Forget it, Brewer said.

Neither A-lister has the massive public following Oprah had in 2007, when her book club was turning authors into overnight best-sellers and a good word from her caused products to fly off the shelf. The talk show host was then ranked by Gallup as one of America's most admired and likeable people.

So, if Oprah's influence was limited, it's not likely that any of the current crop of celebrity endorsers is going to be an election game changer, Brewer said.

Still, the candidates do enjoy parading around with big-name stars.

Obama invited a string of celebrity speakers to the Democratic National Convention this summer, including Eva Longoria of "Desperate Housewives" and actresses Scarlett Johansson and Natalie Portman.

Clint Eastwood made a cameo appearance just ahead of Romney at the Republican National Convention and performed an "empty chair" routine that immediately went viral.

When it comes to fundraising, though, celebrities are indisputable champs, especially for the Democrats, the Center for Responsive Politics found. The campaign finance watchdog reports that Obama received $655,354 in contributions from 184 sports, film and television stars. Romney received $33,500 from nine stars.

But celebrities raise much more than they give themselves, particularly for Democrats. Clooney hosted an event for Obama that raised $15 million. Actor Robert Duvall headlined a Romney fundraiser in Virginia horse country that netted $800,000.

"Democrats," Brewer said, "have a long history of raising some pretty big money from Hollywood."