Vermont Sen. Bernie Sanders has some advice for those considering casting a “protest” vote for a third-party candidate in the upcoming presidential election.

“This is not a governor’s race, it’s not a state legislative race, this is the presidency of the United States,” Sanders told the hosts of MSNBC’s Morning Joe on Friday. “And I would say to those people out there who are thinking of the protest vote, think about what the country looks like and whether you’re comfortable with four years of a Trump presidency.” Sanders, the longest serving Independent member of Congress in U.S. history, was on the show making the case for voting for his former opponent in the Democratic primary Hillary Clinton.

“Let us elect Hillary Clinton as president, and the day after, let us mobilize millions of people around the progressive agenda,” Sanders said.

After a grueling primary, Clinton and Sanders made amends in July at the Democratic National Convention, where she became the party’s presidential nominee.

When asked about Clinton’s lack of support from younger voters, a group that leaned very heavily towards Sanders in the primary, the “Democratic socialist” had more counsel.

“I would just simply say to the millennials and to anybody else, look at the issues. Don’t get hung up on Trump’s kids and whatever the story of the birther issue,” Sanders told Morning Joe. “Stay focused on the issues of relevance to your life. I think Clinton is, far and away, the superior candidate.”

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