Conversely, twentysomething celebrities such as Johansson and Ferrara could draw young voters who've been largely absent from presidential races. "Celebrities are rarely a key in someone's voting decision, but one of their biggest values is attracting new voters to at least listen to a candidate or attend an event," says David Burstein, founder of advocacy group 18 in '08. "Bringing new voters into the process, engaging young people any way they can be engaged, these are good things for democracy."
Early celebrity support focusing on a potential winner is somewhat of a departure from recent elections. "With a lot of celebrities, it's been more a case of who they identify with instead of who they think can actually be elected," notes Schroeder.
Electability was a common theme among many of Edwards' star supporters, who believe voters will ultimately reject Clinton as too polarizing to win a presidential race and Obama's African-American ethnicity and youth as too great to overcome, at least for 2008.
"You have to think beyond the caucuses and the primaries to the general election," Smart says. Sarandon, who initially supported Obama and donated to his campaign before switching to Edwards, said in an interview last week, "Edwards is the only authentic electable candidate" among Democrats.
But Edwards' withdrawal demonstrates that the question of electability ultimately rests in the electorate, not in endorsements. "At the end of the day, a celebrity will get you noticed, but you still have to deliver a compelling message that resonates with voters," Vorhaus says. "And that message has to resonate with more people than your competition."
David Jackson contributed to this report.