Sen. Bernie Sanders Bernie SandersJacobin editor: Primarying Schumer would force him to fight Trump's SCOTUS nominee Trump campaign plays up Biden's skills ahead of Cleveland debate: 'He's actually quite good' Young voters backing Biden by 2:1 margin: 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 Clinton Hillary Diane Rodham ClintonJoe Biden looks to expand election battleground into Trump country Biden leads Trump by 12 points among Catholic voters: poll The Hill's Campaign Report: Biden goes on offense MORE for the Democratic nomination, said on NBC's "Meet the Press" when asked whether he thinks that threshold is fair.

Libertarian nominee Gary Johnson Gary Earl JohnsonWhat the numbers say about Trump's chances at reelection Presidential race tightens in Minnesota as Trump plows resources into state The Hill's Campaign Report: Biden condemns violence, blames Trump for fomenting it l Bitter Mass. primaries reach the end l Super PAC spending set to explode 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.