Sen. Bernie SandersBernard (Bernie) SandersBiden: Trump administration 'coddles autocrats and dictators' Warren and Sanders question Amazon CEO over Whole Foods anti-union video Dem lawmaker to Saudis: Take your oil and shove it 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 ClintonMueller's team asking Manafort about Roger Stone: report O'Rourke targets Cruz with several attack ads a day after debate GOP pollster says polls didn't pick up on movement in week before 2016 election 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 JohnsonThird-party voters made it difficult to predict 2016, says pollster A Senator Gary Johnson could be good not just for Libertarians, but for the Senate too Clinton would beat Trump in landslide in 2016 re-run, says Hill.TV poll 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.