Mr. Sanders’s campaign manager said if Mr. Sanders is the nominee, candidates running on the same ticket need to “buck up” and make the case for Medicare for All.

“If he is the nominee, I think, with all due respect to all the members of Congress out there, and all the candidates, they can take their leads from him. He will chart the path and all they’ll need to do is be strapped in behind,” said Faiz Shakir, Mr. Sanders’s campaign manager…

“If Joe Biden is the nominee, Democrats probably won’t have to be talking about Medicare for All,” said David Wasserman, who analyzes House races for the nonpartisan Cook Political Report. “If Elizabeth Warren is the nominee, then Democrats might have to spend some money distancing themselves from her proposals.”…

“Making this election about whether you support Medicare for All is very damaging up and down the ballot,” said Ms. Hawn. She said the issue may please base voters but the centrists and independents that moderate Democrats rely on to win re-election aren’t ready to eliminate private health insurance.