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.