MINNEAPOLIS - From TV to Twitter, Facebook to YouTube, it seems more celebrities are chiming into this presidential election than ever before. So we wondered, what effect does a celebrity endorsement have on a race?

First off, celebrity political endorsements are nothing new.

You can go back to the 1920s when Mary Pickford stumped for Warren Harding. Paul Newman helped Gene McCarthy in 1968. John Wayne backed Nixon the same year.

“Where celeb endorsements matter most is during the primary season,” said USC history professor Steve Ross, who wrote the book Hollywood Left and Right: How Movie Stars Shaped American Politics.

Ross says celebs are most effective at drawing crowds, getting donations, and influencing youth, especially in lesser known candidates.

“Bernie Sanders was unknown, really unknown, but the Red Hot Chili Peppers aren't unknown, Foo Fighters aren't unknown. Wilco is not unknown,” he said.

Commercial endorsements apply the same theory. Just google Bo Jackson Nike shoe deal.

How much can celebrities influence voters? Consider Oprah Winfrey’s endorsement of then Sen. Barack Obama in 2008.

“They actually found, scientifically, that her endorsement carried 1.1 million votes across the primaries. And they did an analysis of each primary and found those votes were enough to shift primaries in a number of states and give him enough votes to get the ballots,” said Ross.

It’s unrealistic to think any celebrity endorsement of Donald Trump or Hillary Clinton will create a similar impact as Oprah’s endorsement eight years ago.

But candidates are angling for undecided votes to tip the scale, and celebs—like it or not—can add weight to voters' decisions.