Projections from AP and ABC called the race as polls closed, with less than 1 percent of precincts reporting.

Sanders had a 40-point lead in pre-election polls in his bid for a third Senate term from Vermont, one of the most Democratic-leaning states in the nation.

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Sanders, whose views represent the progressive flank of the party, is considered a likely contender for the 2020 Democratic nomination. His push on issues such as "Medicare for all" have shaped the debate within the Democratic establishment.

Zupan, who ran on an anti-regulation platform, had actually lost the GOP primary to H. Brooke Paige, but the GOP state committee put him on the ballot anyway after Paige withdrew his candidacy.