“This guy who’s on the commercials — Jim, what’s his name?” she said, referring to Tom Steyer. “I like what he’s saying. I like the issues he’s bringing up. But why are you spending $3 million on TV when you could be giving the money to Joe?”

Some people are suffering from general political angst. Others have specific qualms: a concern that their favorite candidate lacks that essential quality, electability; a worry that fellow Democrats will become disillusioned if their chosen candidate fails to get the nomination and will vote for a third-party candidate, or for Mr. Trump, or for no one at all — the “Bernie or Nobody” scenario.

A sampling of interviews with Democrats in different parts of the country reveals that worry comes in many forms.

From Jobetta Hedelman-Beaver, 39, of Kennewick, Wash.: “I’m anxious about Trump. I’m super-anxious about him. I blame him for my high blood pressure.”