Some worry that a national ticket led by a septuagenarian democratic socialist who wants to transform government will alienate the political center — not only helping Trump win a second term, but also erasing recent gains by centrist Democratic lawmakers in suburban areas.

If Sanders “wins the nomination, Trump will be president again,” said Rep. Kurt Schrader (D-Ore.). “I will guarantee it.”…

Sanders’s supporters say voters are deeply frustrated and looking for a leader who will shake things up. They note that 11 percent of general-election voters who picked Sanders in the 2016 Democratic primary went on to vote for Trump that November, according to the American National Election Studies survey. An additional 8 percent voted for minor-party candidates, and Sanders’s camp argues he has a shot with them as well.

Anita Cox, a 52-year-old teacher who attended the Sanders meeting in Indiana on Saturday wearing a “Feel the Bern” button, said she knows Trump voters whom she says Sanders could win over. “Maybe they believed his lies,” Cox said.