Sen. Bernie SandersBernard (Bernie) SandersCoal supporter Manchin named top Dem on Senate Energy Committee Gillum to speak at gathering of top Dem donors: report O'Rourke edges out Biden in MoveOn straw poll MORE (I-Vt.) on Sunday said the percentage of popular support candidates need to participate in the presidential debates should "probably" be lower than what it is now.

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"Probably too high," Sanders, who challenged Hillary ClintonHillary Diane Rodham ClintonRoger Stone challenges Dems to produce WikiLeaks evidence Steve King asks Google CEO for names of employees to see if they're liberals O'Rourke edges out Biden in MoveOn straw poll MORE for the Democratic nomination, said on NBC's "Meet the Press" when asked whether he thinks that threshold is fair.

Libertarian nominee Gary JohnsonGary Earl JohnsonHillicon Valley: Social media struggles with new forms of misinformation | US, Russia decline to join pledge on fighting cybercrimes | Trump hits Comcast after antitrust complaint | Zuckerberg pressed to testify before global panel Ex-Facebook exec ousted from company sparked controversy with pro-Trump views: report Heinrich wins reelection to Senate in New Mexico MORE and Green Party nominee Jill Stein have been making a case for why they should be allowed to take part in the presidential debates.

To participate, a candidate needs to hit an average of 15 percent in polls conducted by ABC/Washington Post, CBS/New York Times, CNN/Opinion Research Corporation, Fox News and NBC/Wall Street Journal.

Stein said Sunday morning that the American people have a right to vote and to know for whom they can vote. 

A recent poll by Morning Consult showed that a majority of voters say Johnson should take part in the presidential debates. Nearly 50 percent say the same of Stein.

But neither candidate appears to be polling high enough at this point to participate in the presidential debates.

According to the RealClearPolitics average of polls, Johnson is polling at 7.8 percent and Stein at 3.1 percent.