They Were at the Capitol on Jan. 6. Now They’re Running for Congress.

WASHINGTON — As rioters stormed the Capitol on Jan. 6, 2021, Derrick Van Orden, a retired Navy SEAL, had a front-row seat to the mayhem, perching on the grounds beside a tall, intricately carved, sandstone lantern pier.

J.R. Majewski, an Air Force veteran from Ohio, was also at the Capitol that day, alongside a live-streamer who frequently elevates the QAnon conspiracy theory. So was Sandy Smith, a self-described entrepreneur and farmer from North Carolina who attended former President Donald J. Trump’s speech at the Ellipse and then marched up Capitol Hill.

“I still stand with President Trump and believe he won this election!” Ms. Smith wrote on Twitter the night of Jan. 6, 2021. She had posted that afternoon that she had come to Washington to “#FightForTrump.”

All three are seeking to return to the Capitol next year — this time as members of Congress.

Nearly two years after the deadly attack, which sent lawmakers and the vice president fleeing for their lives, people who were on hand for the riot are seeking to become members of the institution that the mob assaulted. They are running for Congress in competitive districts, in some cases with the support of Republican leaders.

None of the candidates have been charged with entering the Capitol or otherwise engaging in illegal behavior. And almost all of them have sought to distance themselves from the events of Jan. 6 and denounced the violence they witnessed.

But their presence on the ballot is the latest sign of how the extreme beliefs that prompted the Capitol assault — which was inspired by Mr. Trump’s lies of a stolen election and fueled by a flood of disinformation — have entered the G.O.P. mainstream. And it underscores how Republican leaders whose lives were in peril on Jan. 6 are still elevating those voices in the hopes of taking control of the House.

Historically, party leaders have sought to recruit mainstream, broadly appealing candidates to run in competitive districts, wary of alienating independent and moderate voters whose support is typically needed. In many areas of the country, House Republicans have followed that model, elevating diverse candidates with compelling personal stories.

But as they near the prospect of winning back the House majority, Republican leaders have also thrown their backing behind extreme right-wing candidates who are devoted to Mr. Trump and have been active in his political movement, including his efforts to overturn his 2020 defeat.

A handful of them answered his call to march to the Capitol on Jan. 6, as he sought to intimidate members of Congress into rejecting the electoral votes that would confirm Joseph R. Biden Jr.’s victory. Should those candidates prevail in the midterm elections, they would grow the ascendant ranks of hard-right lawmakers who have reshaped the Republican Party in Mr. Trump’s image. And if the party succeed in its drive to retake the House, they would add to the extremist wing of the new majority.

Representative Kevin McCarthy of California, the minority leader who is in line to become House speaker if Republicans prevail, campaigned last month for Mr. Majewski in Fremont, Ohio. Mr. McCarthy criticized an ad by Representative Marcy Kaptur, the veteran Democratic incumbent, that portrayed Mr. Majewski as an extremist who broke through police barricades at the Capitol on Jan. 6.

“Is she running any advertisements of something she’s accomplished, of how she’s made this district better? Or is she trying to say something that’s not true about J.R.,” Mr. McCarthy said, according to The Toledo Blade.

Ms. Kaptur’s ad appeared to refer to a conversation in a Jan. 6 livestream in which Mr. Majewski’s friend said that the two had walked “all the way to the base of the Capitol building” after seeing another group of people crossing a line of barriers. The conversation was reported by Media Matters, the left-leaning watchdog group.

Mr. Majewski has repeatedly maintained that he “committed no crimes” and “broke no police barriers.”

Mr. McCarthy’s support for Mr. Majewski reflects the Republican leader’s sometimes uneasy alliance with the more extreme elements of his party, which he has courted and empowered as part of his push to win the House, even as he has tried to keep them in check.

The super PAC associated with Mr. McCarthy, for example, tried to quash Ms. Smith’s candidacy, pouring nearly $600,000 into negative ads about her. But when she prevailed in her primary, the House Republican campaign arm added her to its Young Guns program, which is intended to help up-and-coming candidates in competitive races.

Representatives for Mr. McCarthy, the House Republicans’ campaign arm and the congressional campaigns of Mr. Van Orden, Mr. Majewski and Ms. Smith did not respond to requests for comment.

At least two of the candidates — Mr. Van Orden and Mr. Majewski — have strong chances of winning their races. Mr. Van Orden lost the seat in 2020 by less than three percentage points when he ran in the same district in western Wisconsin against Representative Ron Kind, a Democrat. Mr. Van Orden, who has the endorsement of all three top House Republicans, is the favored candidate now that Mr. Kind is retiring.

The Daily Beast reported last year that Mr. Van Orden was at the Capitol on Jan. 6.

Mr. Van Orden wrote in an op-ed in The Lacrosse Tribune that he had traveled to Washington “for meetings and to stand for the integrity of our electoral system as a citizen.” He wrote that he “watched what should have been an expression of free speech devolve into one of the most tragic incidents in the history of our nation.”

“When it became clear that a protest had become a mob, I left the area, as to remain there could be construed as tacitly approving this unlawful conduct,” Mr. Van Orden said. “At no time did I enter the grounds, let alone the building.”

The race between Mr. Majewski, who first attracted attention for painting his lawn to look like a Trump campaign banner, and Ms. Kaptur, who has served in Congress for 40 years, is widely seen as a tossup.

Mr. Majewski, who has frequently appeared on shows with a live-streamer who pushes a host of baseless far-right theories, went to the Capitol on Jan. 6 with a QAnon blogger. He said in an interview with a local radio station that he helped bring “60 or 70 people” to the Capitol that day.

“I had multiple people get injured, but I made sure they made it back to our hotel,” Mr. Majewski said. “It was a terrible experience. It was one that was supposed to be great.”

Several other Republican congressional candidates who were at the Capitol on Jan. 6 have been defeated in their primaries or in some cases disqualified. Jason Riddle’s attempt to run in New Hampshire was scuttled when he was sentenced to 90 days in prison after he admitted to entering the Capitol and taking a bottle of wine and a book.

But others, like Ms. Smith, have made it through, in victories that Democrats hope to exploit in the general election. Ms. Smith is running in a district in North Carolina whose partisan tilt has trended only slightly toward Democrats — exactly the type of seat that Republicans are hoping to pick up this election cycle. But her fringe views have led political prognosticators to rate the race as leaning more decisively toward Democrats.

In a Twitter post in December 2020 that was first reported by The Assembly, a local digital magazine, Ms. Smith said that Mr. Trump should be returned to office and the “perpetrators of this fraud” should be arrested. She also called for “Trails & executions of those found guilty of treason.”

Roger J. Stone Jr., a longtime political operative and Trump adviser, endorsed Ms. Smith because she was “the only candidate who has pushed for a full forensic audit of the 2020 election,” he said.

“We need to bring our ‘A Game.’ And pray,” Ms. Smith wrote on Jan. 5, 2021. “If everyone does their part we will be ok. #MAGA #StopTheSteal.”

In a fund-raising email sent four days after the Capitol riot, Ms. Smith confirmed that she had attended the “Stop the Steal” rally.

“It was exhilarating to speak to people from all over the country, from all walks of life,” she wrote. “They just wanted to be heard and support their president — none were inciting violence.”

She continued: “I don’t support violence in any way. But we need to make the D.C. establishment listen!”

She has since been endorsed by half a dozen sitting members of Congress.