Harry Dunn, a former Capitol Police officer whose pitched battles with former President Donald J. Trump’s supporters on and after Jan. 6, 2021, vaulted him to political stardom, was greeted Tuesday evening in Annapolis, Md., like a celebrity.

But there was also an undercurrent of skepticism among attendees at the Beacon Waterfront Restaurant, where he appeared at a campaign event to bolster his candidacy for the U.S. House.

“We have a person here with a proven legislative record,” Jessica Sunshine, an Annapolis Democrat, told Mr. Dunn, referring to State Senator Sarah Elfreth, his main opponent in next month’s Democratic primary. But, she added, “You have heart.”

But Mr. Dunn, an imposing former offensive lineman who stands 6-foot-7-inches and 325 pounds, didn’t shy away from the reason he is running: to save what he sees as democracy on the edge. “This moment, right now? It calls for a fighter,” he said.

He is not the only one making that case to Democrats.

Over the next three months, primaries in three Mid-Atlantic House districts — from the exurbs of Washington, D.C., to Harrisburg, Pa. — will test the strength of Jan. 6 memories and whether the battle cry of “save democracy” will be enough even for Democratic voters who have many other concerns.

For many voters, partisan celebrity is virtually the only factor in their support for candidates like Mr. Dunn, who played a starring role in the Jan. 6 hearings, and Yevgeny Vindman, who goes by Eugene and along with his identical twin brother, Alexander, played a key role in highlighting Mr. Trump’s effort to strong-arm Ukraine into digging up dirt on Joseph R. Biden Jr.

Margaret Pepin, 71, could hardly believe it when Mr. Vindman rang her video doorbell on Tuesday afternoon in Occoquan, Va., and his unmistakable face, made famous during Mr. Trump’s first impeachment, popped on her security screen. “I looked at my Ring. I said, ‘Is it really him?’” she said, acknowledging that she might have confused him for his better-known twin brother. “I am thrilled.”

The celebrity-candidate factor has allowed the “save democracy” candidates to raise so much money nationally that these less-experienced Democrats will dominate the airwaves. But with issues like abortion, guns, inflation and immigration competing for attention, their victories are not guaranteed — even in Democratic primaries where a threat to democracy will be a key issue in a year with Mr. Trump on the ballot.

“There are certainly a small subset of folks that it is not enough for,” Mr. Vindman said of his campaign’s focus. “But the vast majority of folks do think that democracy is the most important issue, because they see it very much like I see it. Every other issue is rolled into it.”

The voters will soon get their say.

In Pennsylvania, Democratic voters will go to the polls on April 23 to choose from among the two leading candidates, Janelle Stelson and Mike O’Brien, and four others, all hoping to take on Representative Scott Perry, a conservative Republican who was deeply entangled in Mr. Trump’s effort to remain in power after he lost the 2020 election.

Mr. O’Brien, a former Marine Corps officer and fighter pilot, has made the preservation of democracy central to his candidacy. Ms. Stelson, a former television news broadcaster with strong name recognition, has made that issue one of many.

Mr. Dunn is one of 22 Democrats vying to succeed Representative John Sarbanes, who is retiring, in Maryland’s May 14 primary that will almost certainly decide the next House member for the state’s heavily Democratic Third District. His opponents include Ms. Elfreth, a state senator with the backing of the American-Israel Public Affairs Committee, two veteran members of the Maryland House of Delegates, and a prominent gun control activist.

Mr. Vindman — another new candidate — is seeking to replace Representative Abigail Spanberger, who is running for governor and hopes primary voters in her marginally Democratic district will side with him on June 18 over seven other Democrats.

Mr. Vindman, an Army colonel who was fired from Mr. Trump’s National Security Council for his connection to the first impeachment investigation, and Mr. Dunn, the former Capitol Police officer, have become darlings of the Democratic activist set, parlaying fame into huge fund-raising advantages.

The money has followed the ‘save democracy’ movement.

Mr. Vindman raised more than $2 million through the end of last year, $1.5 million from donors whose contributions were too small to require disclosure. Those with larger gifts include Tom Daschle, the former Senate majority leader, and the actor Mark Hamill, known widely for playing Luke Skywalker and more narrowly as an ardent foe of Mr. Trump.

His closest fund-raising rival, Margaret Franklin, a Prince William County supervisor, raised $122,894.

Because Mr. Dunn did not formally begin his campaign until January, he has not yet had to disclose his fund-raising numbers, but campaign officials say he will announce totals for the first quarter next week nearing $3.7 million. His closest competitor, Ms. Elfreth, raised just over $400,000 last year, but has significant financial support from outside groups.

Not surprisingly, the celebrity candidacies of Mr. Vindman and Mr. Dunn have raised some hackles among elected Democrats who had served in local offices waiting for a chance to run for the House. In both races, women, many of them minorities, are feeling particularly aggrieved.

“Yes, this campaign is about saving democracy, but it’s also about reclaiming civil, human and women’s rights gains that people fought and died for, and that are being lost,” said Terri L. Hill, a physician who has served in the Maryland House of Delegates for nearly a decade.

“I have great respect for his heroism,” she said of Mr. Dunn. “I really respect what he did on Jan. 6, 2021, but I’m really focused on Jan. 6, 2025,” when the next Congress takes office.

The race for Maryland’s Third District may be the purest version of the tension between the celebrity and the laborer, with Mr. Dunn, a political newcomer, facing Ms. Elfreth, an experienced legislator who has secured 84 bills since being elected as the youngest female state senator in Maryland history in 2018.

Mr. O’Brien called Mr. Perry’s role in the 2020 effort to overturn the election his “No. 1 issue,” and believes voters agree. “In the primary, Democrats do care first and foremost about democracy itself,” he said.

But with the April 23 primary just weeks away, Mr. O’Brien is considered the underdog against Ms. Stelson, who is more nuanced as she talks about women’s rights, abortion access and the price of gasoline and groceries.

“It’s certainly a large part of the story,” she said of Jan. 6 and Mr. Perry. “It’s not the whole story.”

But for national Democrats, the district with the most at stake might be in Virginia, since the party cannot afford to lose a seat it now holds. Democratic opponents fret over Mr. Vindman’s vulnerabilities — he’s a relative newcomer to Northern Virginia, voting for the first time there in 2022.

His 25 years of service as an Army lawyer should serve him well even with some Republican voters in a district with four military installations, he said. But at times he slips into the language of the ardent Trump foes who have embraced him.

“Are there going to be folks who hate my guts for what I did to their orange prophet?” he asked, referring to Mr. Trump. “Undoubtedly.”