Sen. Bernie SandersBernie SandersFive takeaways from Trump's 2020 kickoff rally Five takeaways from Trump's 2020 kickoff rally Sanders tears into Trump in response to campaign kickoff rally 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 ClintonFive takeaways from Trump's 2020 kickoff rally Five takeaways from Trump's 2020 kickoff rally Trump jokes he'd get 'electric chair' if he deleted even one 'love note' email to Melania 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 JohnsonAmash won't rule out Libertarian challenge to Trump Buzz grows Amash will challenge Trump as a Libertarian Potential GOP primary challenger: Trump's 'contempt for the American people' behind possible bid 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.