This week the rock star Jon Bon Jovi hosted a fundraiser for Mr Kerry at his New Jersey home at which 300 guests raised more than $1 million (540,000) for the Kerry campaign. Mr Kerry, underlining the importance and financial muscle of the celebrity endorsement, flew in by helicopter for the event.
Speaking at the fundraiser, the singer acknowledged the drawbacks of dabbling in politics but pledged to continue to back Mr Kerry’s campaign.
"I’ve received hate-mail at my house. I’ve had people drive by my home and shout things out," he said. "And I think that they question my patriotism because I decided to stand up and have a voice. And I stood up to have a voice because I think that’s the most American thing that you can do."
Bon Jovi is not the only celebrity to have pledged support for Mr Kerry. Joining him at the fundraiser were the actors Meg Ryan, James Gandolfini and Steve Buscemi.
The pop musician Moby has joined forces with the liberal pressure group moveon.org and has urged liberals to make their own anti-Bush adverts that can be spread via the internet.
Madonna, who initially endorsed General Wesley Clarke during the Democratic primary campaign, has said of Mr Bush: "Our greatest risk is not terrorism, and it’s not Iraq or the Axis of Evil. Our greatest risk is a lack of leadership, a lack of honesty and a complete lack of consciousness."
Among the fiercer critics of the president is the actor Alec Baldwin, like Barbra Streisand and Martin Sheen a long-standing liberal activist, who has argued: "Everything that Bush touches turns to manure in public policy."
Gwyneth Paltrow recently joined the growing number of A-list stars to criticise the president when she said: "I think George Bush is such an embarrassment to America in the way that he doesn’t take the rest of the world into consideration."
Mr Bush’s campaign is notably less star studded than his rival’s. Although Arnold Schwarzenegger will campaign for Mr Bush in California, his duties as its governor mean he is unlikely to spend much time on the national campaign trail.
Kelsey Grammer, whose hit sitcom Frasier has just concluded its final season, is one of the few stars supporting the president’s campaign for re-election. He acted as master of ceremonies at a Bush fundraiser in March.
Last year Bruce Willis told the president he was willing to volunteer for military service if necessary, only to be told he was too old for active duty.
Four years ago the actors Bo Derek and Chuck Norris were among the few Hollywood celebrities to campaign openly for Mr Bush, although neither has so far appeared in the president’s 2004 campaign.
This Bush campaign season has been almost equally star-free, although the pop singer Jessica Simpson has sung at Republican fundraisers. Former Beverly Hill 90210 star Shannen Doherty also calls herself "a big fan of President Bush".
While the Clinton years saw a procession of celebrities staying overnight at the White House, Mr Bush’s residency has been largely celebrity-free. White House records show that the golfer Ben Crenshaw is one of the few celebrities who have been invited to stay the night.
Although celebrity supporters can raise a candidate’s profile, their chief use is to attract more voters and sell tickets to fundraising events, argues Alan Schroeder, professor of journalism at Northeastern university in Boston and author of Celebrity-in-Chief: How Show Business Took Over the White House.
"An upside to celebrity endorsement of a candidate is that a star can glamorise a campaign. Someone like John Kerry, who’s not the most charismatic politician, can, by associating with a celebrity, make himself look like a celebrity," he said.
Such endorsements can also pose a danger, as Gen Clarke discovered this year when the campaign was forced on to the back foot following comments from the film-maker Michael Moore, who supported Ralph Nader in the 2000 elections.
After backing the former NATO commander, Mr Moore accused Mr Bush of being a deserter. Gen Clarke was asked if he associated himself with the allegation, a story that ate up valuable airtime and newsprint, preventing his campaign from communicating a more positive message.
Although celebrity support can win a candidate free extra media coverage, it is not likely to be a factor when voters decide who to vote for.
According to Larry Sabato, director of the Centre for Politics at the University of Virginia: "My take on celebrity endorsements is that the only weak minds they can sway are fortunately not registered voters, or they don’t show up at the polls."