Star power is especially bright for Democrats, who've lost five of the past seven presidential elections. Campaign rallies aside, celebs have worked phone banks, canvassed door to door, shaken hands at local diners, attended union gatherings and hit countless small towns and communities to spur support.
"They have been very generous with their time and resources, and I'm grateful for the help they have provided this campaign," Clinton said hours after winning Tuesday's Florida primary. "They understand that this election is too important to sit on the sidelines."
Fresh off Tuesday's Florida primary win, Clinton staffers are plotting how best to deploy celebrities in preparation for Super Tuesday. Aside from the current cast, "we've got a lot of new people coming," says spokesman Jin Chon.
Celebs aren't naive enough to think they sway voters. "No one should give more credence to (celebrity) opinions than anyone else," says Designing Women star Jean Smart, who was an Edwards backer. "I'm no Oprah. But if I can get people to come out, even if it's just out of curiosity, that's fine."
But "they help to draw crowds," Edwards said in an interview last week. "That's the most important thing they do: bring attention."
Republican Rudy Giuliani, who also withdrew from the race on Wednesday, had actor Jon Voight accompanying him. "This election is the most important of my lifetime," the actor and lifelong Democrat recently said.
Observers cite Winfrey's early praise and fundraising efforts for Obama for bringing fellow celebrities to primary races.
"It's the Oprah factor," says public relations and crisis management strategist Robbie Vorhaus. "It hasn't been that long since celebrities might have felt their careers were in jeopardy if they made a political stance. Now they're realizing the fate of the world, in many respects, is in the balance. The fact that Oprah went out and got behind a candidate opened the door for celebrities and other people of influence to stump for candidates."
Some celebrities, such as Obama-supporter George Clooney, have stated that some campaign work might do more harm than good, because Hollywood's left-leaning image doesn't always play well in middle America.
There's also the risk to an actor's own career. Desperate Housewives' Denton, a long-time Republican who canvassed door to door for Edwards in New Hampshire, toured colleges in Iowa and stumped in Nevada and South Carolina, has already felt some backlash.
"I've gotten a surprising amount of mail from unhappy fans, some real conservatives who say that they're disappointed in you and will never watch your show again," he says. "It's been eye-opening."
There's also the risk of a TMZ-type moment. At a fundraiser at his Texas ranch this month, Norris told reporters that Huckabee rival McCain, who's 72, was too old for the presidency. McCain later responded that he'd send his 95-year-old mother to "wash Chuck's mouth out with soap."
"This is the problem you can run into," says Boston University professor Alan Schroeder, author of Presidential Debates: 40 Years of High Risk TV. "Celebrities don't edit themselves."
Interviewed last week on cable channel MSNBC, Norris, 67, admitted he'd made a mistake and said he had apologized to McCain. "I don't go in as a celebrity," Norris told USA TODAY. "I'm just a concerned citizen. I'm concerned about the future of our country."