Support among Democratic voters for opening an impeachment inquiry is growing, and at least 100 members of Congress are now in favor. But even in the aftermath of Mr. Mueller’s nationally televised testimony, voters bring up impeachment far less than they do policy issues, and few of the 2020 hopefuls make it central, or mention it at all, in their appeals.

Interviews with Democratic primary voters in New Hampshire and Wisconsin, and at the N.A.A.C.P. and Urban League conferences this week, yielded an unwavering belief that Mr. Trump is a lawless demagogue who must be turned out of office — but also a sense that efforts to impeach him will inevitably run aground in the Republican-controlled Senate.

“I think they should do an inquiry,” said Mary Ann Lakevicius, a Concord, N.H., resident who came to see Ms. Warren on Saturday. “But I think Nancy Pelosi is right: If they can’t get it through the Senate, what’s the point?”