Political conventions these days are less about choosing a candidate than they are well-orchestrated shows aimed at getting the party's message and candidate out to the country.
Just Tuesday, Obama raised nearly $5 million at a celebrity-packed fundraiser in Los Angeles. The same day, George Clooney pulled in up to an additional $900,000 for the Democratic candidate at a fundraiser of American citizens in Switzerland.
"The two things you need to win are money and people's attention, and celebrities can get you a little of both," said Steve Ross, chairman of the history department at the University of Southern California.
While celebrities have donated plenty of money to campaigns, their real value comes in the ability to draw crowds.
"Once people turn out, they actually listen to the campaign speech," said Ross, who is finishing a book called "Hollywood Left and Right: How Movie Stars Shaped American Politics."
Democrats have traditionally had a larger showing of stars and this year is no different. Celebrities from Oprah Winfrey to Ben Affleck to Kareem Abdul-Jabbar have come out in support of Obama.
The Republicans have had their fair share of stars too, with Heidi Montag, Stephen Baldwin, Wilford Brimley, Kelsey Grammer, Jon Voight and Sylvester Stallone all backing McCain.
But overall, the television, film and music industries have been leaning heavily toward Democrats this year, according to an analysis by the Center for Responsive Politics.
Obama received more than $4.8 million and Hillary Clinton, his main challenger in the Democratic primaries, took in another $3.6 million from the industries as of Aug. 20.
McCain got less than $900,000.
The actual donations from movie stars make up just a small amount of the overall cash needed to run for president. Consider this: Obama has raised $389 million to date and McCain has taken in $174 million.
"The biggest givers in politics are not celebrities," said Massie Ritsch, spokesman for the center. "They are most commonly Wall Street bankers, lawyers, lobbyists and corporate executives."
It's just that celebrities tend to get more attention than other donors, Ritsch said.
"If anything," he added, "they are probably most valuable to a campaign as headliners for fundraising events that bring in more donors."
Democratic fundraiser Donna Brazile said celebrities are visible and help attract support that isn't otherwise always available to candidates.
"As technology expands how campaigns are both covered and managed, celebrities can help well-known candidates appear like ordinary people," she said in an e-mail. "In the final days of the Gore campaign, Bon Jovi traveled nonstop with the candidate on a tour of Michigan. People came to see Gore, but also hear Bon Jovi. What a two-fer for any candidate seeking both the spotlight and to raise much needed funds."
"When celebrities do anything, people pay attention," Robert Thompson, director of the Bleier Center for Television and Popular Culture at Syracuse University, said. "It's one of the ways you can shoehorn yourself into more media attention."
Thompson equates the political endorsements to what those celebrities do for sneakers, sports drinks and cars.
"They are the perfect Trojan horse," he said. "Cameras tend to be magnetically attracted to them."
A candidate who is seen "as an old foggy" can benefit from Hollywood associations, he said.
During the 1968 presidential race, Richard Nixon made a brief appearance on the popular TV show "Laugh-In," asking "Sock it to me?" Several people have credited that appearance with helping Nixon win the White House.
Bill Clinton started out as "the Hollywood, rock and roll president," Thompson said. "It eventually began to play against him."
Thomspon said Obama already has charisma, is attractive and seen by some as a rock star.
"There's a campaign that doesn't need the kind of things that celebrity can deliver," he said.
Ultimately, however, endorsements don't lead diehard political supporters to switch affiliations.
"In most cases, celebrity endorsements tend to make you change your mind about the celebrity, not the candidate," Thompson said.
New York venture capitalist Alan Patricof, a major Clinton fundraiser, said Democrats and Hollywood stars agree on many issues.
"It seems traditionally they've been more progressive in their thinking and less conservative," Patricof said of the celebrities.
Not all stars are Democrats. Charlton Heston supported several conservative causes and was president of the National Rifle Association. John Wayne was also involved in Republican politics. But for the most part, "celebrity types seem to gravitate toward the ideals of the Democratic Party," Patricof said.
Celebrities aren't working the phone banks making calls for donations. But when they appear at an event, he said, that gives it "star power" and helps draw a larger crowd of donors.
"Their name associated with an event helps sell more tickets," Patricof said. "They're tapping into the traditional network, [which] energizes and mobilizes it. … They're an important element. Without them, some events would be difficult to get off the ground."
While celebrities might be more noticeable these days, they have been part of politics for decades.
Ross said the earliest example he came across in his research is Mable Normand, who backed the Socialist candidate for Los Angeles mayor in 1913. (Normand starred in movies with Charlie Chaplin and has been credited with being the first person to throw a cream pie in films.)
Another early Hollywood player in politics was Louis B. Mayer, co-founder of film studio MGM. He was a head of the California Republican Party and played an active part in Herbert Hoover's presidential campaign.
The 1960s cookbook "Many Happy Returns: The Democrats' Cook Book, or How to Cook a GOP Goose" included an introduction by Frank Sinatra.
"Not only should every Democrat own a copy of this book, but he should load up all his or her friends, and even smuggle some copies into Pasadena and other points where the enemy is strong and square," he wrote.
The cookbook is just one example of how stardom and politics really merged in the 1960s, especially for the Democrats thanks to the campaign of John F. Kennedy.
Today, Democrats and big-name Hollywood stars are very much in line. Conservatives like to point out this alliance when talking about left-wing conspiracies.
Even the Simpsons have taken note of the disparity between the Democratic and Republican support from Hollywood. In January, the cartoon sitcom had both parties courting character Ralph Wiggum to run on their ticket for president.
Political blogger Arianna Huffington, portrayed on the show as a Democratic operative, told Wiggum: "Ralph, darling, be a Democrat. We have Alec Baldwin. They have Stephen Baldwin. They might as well not even have a Baldwin."
Ross said that while there might be fewer Republican stars in politics, those that enter tend to be more active and actually run for office themselves. Democratic stars tend to lend their names to others' campaigns.
"They don't want to give up their careers for their politics," Ross said.
Big name Republicans who have held office include Sonny Bono, Ronald Reagan and Arnold Schwarzenegger.
When Obama accepted the nomination last week, he did so in a stadium packed with 80,000 delegates, supporters and what some people called "fans." The crowd was entertained by Sheryl Crow, Stevie Wonder, will.i.am and John Legend.
Obama in particular risks being seen more of a rock star than a commander in chief, and McCain has been quick to seize on Obama's links with celebrity. Last month, he aired an attack ad characterizing Obama as a peer of Britney Spears and Paris Hilton.
Additionally, a candidate's choice in celebrities can also backfire.
Albert L. May, a professor of media and public affairs at George Washington University, also said that celebrities do not necessarily change people's minds but help draw attention to the candidates' message.
"We are a celebrity-soaked culture and a celebrity-soaked media, and that bleeds over to politics more than in the past, and increasingly so," May said.
But not all celebrity endorsements are a blessing.
Jane Fonda, for instance, said May, has been a controversial and polarizing figure. Heston also was controversial. "They can bring that type of baggage with them."