Katy Perry, Lena Dunham and Jamie Lee Curtis are among the many celebrities hitting the campaign trail for Hillary Clinton this election cycle. The "Duck Dynasty" guys are split on whether they prefer Donald Trump or Ted Cruz as the next president of the United States. But do endorsements from the rich and famous actually do much for campaigns? Or, is it, as traditional political wisdom holds, that endorsements from established party politicians that decide the primary winner?

In their popular book about the 2008 election, The Party Decides, political scientists Marty Cohen, David Karol, Hans Noel, and John Zaller posit that the most reliable indicator for who gets the nomination is who has the most endorsements from the party elite -- elected officials and other politicos.

Right now, Clinton, the Democratic frontrunner, and Jeb Bush, the once-presumed-Republican-nominee-now-laggard-in-the-polls, are leading their respective "endorsement primaries."

And some of the early leaders in their respective camps -- Donald Trump and Ted Cruz on the Republican side and Bernie Sanders on the Democratic side -- are not the parties' favored candidate, to say the least. A cadre of party elite have banded together in a recent magazine special to take Trump down (probably a doomed mission). It's widely known that Cruz is hated within his party (a fact he embraces). And Sanders's top rival for the Democratic nomination, Clinton, far outpaces him in party endorsements

Should Clinton and Bush continue to rack up the support of their colleagues and prevail in the primaries, traditional wisdom will also win the day. But what if Trump, Cruz or Sanders win? Or some other, less-favored candidate? 

One way to look at it would be that things have changed for some reason, that 2016 is different. Another would be that other types endorsements -- those from celebrities, particularly -- actually matter more than is thought. 

"In the primary, you're still trying to find any way to break out of the pack," said Jon Reinish, a Democratic political consultant. A celebrity backer is as good a way as any.

Historically, celebrity endorsements have been shown to do little for candidates in terms of vote-getting. But eight years ago, we saw an exception: Oprah Winfrey. Her backing of then-Senator Barack Obama is estimated to have garnered him approximately one million extra primary votes in the highly-competitive race against Clinton for the Democratic Party nomination.

This election cycle, the primary races among Republicans and Democrats are tight, and a million extra votes would go a long way. But even if they don't drive Oprah-level votes, celebrities still have various ways of giving candidates an advantage.

In the general election, the party idea is so dominant that celebrity endorsements pull little weight and can actually backfire, explained Michael Cobb, associate professor of political science at North Carolina State University and expert in political behavior and public opinion. But in the primaries, the rules can be a bit different.

Take Obama '08. Beyond Oprah's endorsement, the Obama team would bring celebrity backers out on the campaign trail to specific locations based on regional popularity in order to draw larger crowds. His camp would then send volunteers to register voters and get contact information in order to build its social media network and voter database.

"The Obama team was incredibly savvy," Cobb said.

This election cycle, many of the campaigns are likely engaging in similar activities. That certainly appears to be the case with Clinton, who has been joined on the campaign trail with pop star Demi Lovato, soccer player Abby Wambach and investment icon Warren Buffett, among others.

But endorsements and appearances do more than drum up crowds and grow voter databases -- they can also have important secondary effects.

"It generates attention in the news cycle to particular candidates," Cobb said. "So, the ones that can do better are going to potentially get more media coverage because of it."

Trump has dominated the news cycle since announcing his bid for the GOP nod last summer and has hardly needed help from others in directing America's political conversation. But take his most significant endorsement, from former Alaska Governor Sarah Palin.

"She has a political background, but she's become more of a pop culture celebrity rather than a political maker and shaker," said David Perlmutter, dean of media and communication at Texas Tech University.

Her endorsement of the billionaire real estate magnate caused a media frenzy. Moreover, it essentially buried other would-be big political stories, like Iowa Governor Terry Brandstad's warning against Cruz and reports that emails from Clinton's home server contained intel from some of the government's most secretive programs.

Personalities like Palin's and the other celebs can also help candidates appeal to specific demographics and subgroups candidates need.

Reinish pointed to the example endorsements from the cast of reality television show "Duck Dynasty" -- patriarch Phil Robertson, who has made controversial anti-gay remarks in the past, is backing Cruz, while his son, Willie Robertson, has backed Trump. "Those have been hard fought for endorsements to land," he said.

Clinton's support from various celebrities, including music producer Pharrell Williams and pop singer Lady Gaga, is a way for her to increase her appeal among a younger demographic that hasn't immediately warmed up to her bid. "That's significant in today's political and media landscape," said Reinish.

And, of course, celebrities help on the fundraising front, too.

The rich and famous often act as bundlers, organizing and collecting campaign contributions from other donors through fundraisers and other means.

In his 2012 reelection bid, Obama received help from celeb bundlers like Will Smith and Jada Pinkett-Smith, Eva Longoria and Gwen Stefani. This election cycle, singer Cristina Aguilera and talent manager Scooter Braun have raised money for Clinton.

By law, the identities of bundlers do not have to be disclosed unless they personally hand over checks or are registered lobbyists, and most campaigns work to keep such activities behind the scenes. However, in an effort toward transparency, some campaigns choose to disclose who is acting as a bundler on their behalf. Clinton and Jeb Bush have this election cycle. (Interestingly, Palin has sort of flipped the model on its head and is utilizing her Trump endorsement to raise money for her own super PAC.)

With primary voting just days away, contenders are pulling out all the stops to get ahead, and that means getting celebrities in on the game, too. Even Sanders is playing along, with Ben & Jerry's co-founder Ben Cohen announcing he has created a new flavor celebrating the Vermont senator's White House run, called "Bernie's Yearning."

That said, the party's chosen candidates could still prevail. After all, no delegates have yet been awarded. 

"What difference is anyone expecting [celebrity endorsements] to make? No one's voting yet, you can't tell whether they're affecting votes," said Cobb.

"Attention does not equal action," Perlmutter warned.

But do party endorsements translate to nominations? In the past, maybe. In 2016, we'll see.