“It’s a little frustrating to see some candidates coming in — whether Beto or whoever — and start getting a lot of attention when they do not have the same résumé of other candidates,” said Kathy Sullivan, a former New Hampshire Democratic chairwoman who has not yet endorsed in the race. Making clear that her exasperation was on behalf of some of the female candidates, Ms. Sullivan added, “But there’s nothing new about that, we’ve always had to do it backward and in heels.”

Other Democrats worry about what they describe as the political version of post-traumatic stress disorder following Hillary Clinton’s stunning loss. Questions of viability, party officials say, have become overwhelming to the point that activists are uncertain about following their instincts out of fear they will nominate someone who will lose to Mr. Trump.

“We’re so traumatized by 2016 that we’re afraid to trust our hearts and that’s turning us all into pundits,” said Adam Jentleson, a longtime Senate Democratic aide who supports Ms. Warren. “Overthinking and voting for a candidate we like less but who we think other people will like more is the path to ending up with a candidate no one likes very much.”

Mr. Trump, who has long relished taunting Ms. Warren with the “Pocahontas” slur, has already declared victory. In an interview on Fox News last week, Mr. Trump said, “I hit her too hard, too early and now it looks like she’s finished.”

Part of Ms. Warren’s challenge owes to timing — she is not the new candidate on the scene the way she would have been four years ago, when progressives lobbied for her to challenge Mrs. Clinton.

“There were artificially high expectations early on because there was so much interest in her in 2016,” said Jennifer Palmieri, a top aide to Mrs. Clinton in the last race. “Everybody loves you when you’re the one who’s not in the race, and once you get in you’re a mortal and have to slog it out. That doesn’t mean you can’t come back and win — it’s just a different type of race.”