And for the first time, a lawmaker who embraced the rioters may have to answer for his actions in a court of law.

“I don’t think we can have those persons who have engaged in acts of insurrection elected to office and serving in office in violation of their constitutional duties and oath,” said John R. Wallace, one of the lawyers on the case and a campaign finance and election law expert in Raleigh, N.C. He added, “It should not be difficult to prove you are not an insurrectionist. It only seems to be difficult for Madison Cawthorn.”…

If Mr. Cawthorn is labeled an “insurrectionist,” that could have broader ramifications. Other Republican House members, such as Marjorie Taylor Greene of Georgia, Mo Brooks of Alabama, Paul Gosar of Arizona, and Lauren Boebert of Colorado, face similar accusations, but their state’s election laws present higher hurdles for challenges to their candidate qualifications. If one of their colleagues is disqualified for his role in encouraging the rioters, those hurdles might become easier to clear.

The lawyers challenging Mr. Cawthorn’s eligibility are using an amendment last invoked in 1920, when Representative Victor L. Berger, an Austrian-American socialist, was denied his seat representing Wisconsin after criticizing American involvement in World War I.