Third-party presidential candidates are not worth a vote in the 2016 election, according to Bernie Sanders.
At a rally for Democratic congressional candidate, Zephyr Teachout in New Paltz, New York on Friday, the Vermont senator advised voters not to vote for a third-party candidate for president and to remain focused on stopping Donald Trump.
"When we're talking about president of the United States, in my own personal view, this is not the time for a protest vote," Sanders said, according to the The Washington Post. "This is [the] time to elect Hillary Clinton and then work after the election to mobilize millions of people to make sure she can be the most progressive president she can be."
Sanders began campaigning for Clinton after losing the Democratic presidential primary to the former secretary of state.
See photos of Bernie Sanders with Hillary Clinton:
Hillary Clinton and Bernie Sanders together
Hillary Clinton and Bernie Sanders together
Democratic U.S. presidential candidate Hillary Clinton and Sen. Bernie Sanders stand together during a campaign rally where Sanders endorsed Clinton in Portsmouth, New Hampshire, U.S., July 12, 2016. REUTERS/Brian Snyder - TPX IMAGES OF THE DAY
LAS VEGAS, NV - October 13: Bernie Sanders and Hillary Clinton pictured at the 2015 CNN Democratic Presidential Debate at Wynn Resort in Las Vegas, NV on October 13, 2015. Credit: Erik Kabik Photography/ MediaPunch/IPX
Sen. Bernie Sanders, of Vermont, left, and Hillary Rodham Clinton laugh during the CNN Democratic presidential debate Tuesday, Oct. 13, 2015, in Las Vegas. (AP Photo/John Locher)
Democratic presidential candidates Hillary Rodham Clinton, left, Sen. Bernie Sanders, I-Vt., center, and former Maryland Gov. Martin O'Malley, talk backstage before the start of the Iowa Democratic Party's Jefferson-Jackson Dinner, Saturday, Oct. 24, 2015, in Des Moines, Iowa. (AP Photo/Charlie Neibergall)
Bernie Sanders, left, offers an apology to Hillary Clinton during a Democratic presidential primary debate Saturday, Dec. 19, 2015, at Saint Anselm College in Manchester, N.H. (AP Photo/Jim Cole)
Democratic presidential candidate, Hillary Clinton and Democratic presidential candidate, Sen. Bernie Sanders, I-Vt. speak during a break at the NBC, YouTube Democratic presidential debate at the Gaillard Center, Sunday, Jan. 17, 2016, in Charleston, S.C. (AP Photo/Stephen B. Morton)
Democratic presidential candidate, Sen. Bernie Sanders, I-Vt, reacts to Democratic presidential candidate, Hillary Clinton's answer to a question during a Democratic presidential primary debate hosted by MSNBC at the University of New Hampshire Thursday, Feb. 4, 2016, in Durham, N.H. (AP Photo/David Goldman)
Democratic presidential candidates Sen. Bernie Sanders, I-Vt, left, and Hillary Clinton take the stage before a Democratic presidential primary debate at the University of Wisconsin-Milwaukee, Thursday, Feb. 11, 2016, in Milwaukee. (AP Photo/Tom Lynn)
Democratic presidential candidates, Hillary Clinton and Sen. Bernie Sanders, I-Vt, shake hands before the start of the Univision, Washington Post Democratic presidential debate at Miami-Dade College, Wednesday, March 9, 2016, in Miami, Fla. (AP Photo/Wilfredo Lee)
Democratic presidential candidate Sen. Bernie Sanders, I-V.t, right, speaks as Hillary Clinton listens during the CNN Democratic Presidential Primary Debate at the Brooklyn Navy Yard on Thursday, April 14, 2016 in New York. (AP Photo/Seth Wenig)
Democratic presidential candidate Hillary Clinton listens as Sen.Bernie Sanders, I-Vt. speaks during a rally in Portsmouth, N.H., Tuesday, July 12, 2016, where Sanders endorsed Clinton. (AP Photo/Andrew Harnik)
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Sanders was a spoiler for the Democratic nominee during the primary, but has since become an outspoken critic of third-party candidates like the Green Party's Jill Stein and Libertarian nominee, Gary Johnson.
"I know more about third-party politics than anyone else in the Congress, okay? And if people want to run as third-party candidates, God bless them! Run for Congress. Run for governor. Run for state legislature," Sanders said.
Sanders' pitch to elect Clinton has been met with some opposition from his most ardent supporters amid controversy that the Democratic party favored Clinton during the primary.
Outrage from Sanders' supporters gripped the Democratic National Convention in July, where Clinton formally accepted the party's nomination for president.