Sanders voters became Trump voters?
by Ed Sawicki - February 12, 2020
In 2016, approximately 11 to 12 percent of Sanders supporters didn't vote for Hillary Clinton in the general election, voting instead for Jill Stein, Gary Johnson, or Donald Trump. A significant portion of these supporters were people who normally vote Republican. Yes, Republican. Some Republican voters couldn't bring themselves to vote for Trump and were attracted to the policies voiced by the Sanders campaign. See The Atlantic article.
When Sanders didn't win the nomination, these Republican voters, not considering Hillary Clinton to be an acceptable substitute for Sanders, voted for the Republican candidate, as they normally would. This is why you may hear people say that Sanders supporters voted for Trump.
The MSNBC article tells how Sanders consistently did better in the polls against Trump than Clinton, thus supporting the story in the Atlantic.
The Atlantic: The Lifelong Republicans Who Love Bernie Sanders
MSNBC: Why does Sanders do better than Clinton against Trump?