Former Democratic presidential candidate 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 on Sunday discouraged voters from picking a third-party nominee, saying the issues facing the U.S. are too dire for a "protest vote."

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"This moment in history for a presidential election is not the time for a protest vote," the Vermont senator said on CBS's "Face the Nation."

"It's time to look at which candidate will work best for the middle class and working families."

He said he didn't want to disparage third-party candidates, but he encouraged voters to pick Democratic presidential nominee 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 over Republican nominee Donald Trump Donald John TrumpBubba Wallace to be driver of Michael Jordan, Denny Hamlin NASCAR team Graham: GOP will confirm Trump's Supreme Court nominee before the election Southwest Airlines, unions call for six-month extension of government aid MORE.

Libertarian presidential 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 has hoped to benefit from record low favorability numbers for Clinton and Trump. But a RealClearPolitics polling average only gives him 8.9 percent support nationally.