Mr. Bopp, in an interview, declared the matter “the most frivolous case I’ve ever seen,” but allowed that what he called an “unethical” exploitation of North Carolina law by “competent” lawyers could pose a real threat to Mr. Cawthorn — and by extension, to others labeled “insurrectionists” by liberal lawyers.

“This is the real threat to our democracy,” he said. “Just by bringing the complaint, they might jeopardize a member of Congress running for re-election.”

“They have multiple targets,” he added. “It just so happens that Madison Cawthorn is the tip of the spear.”

That is because North Carolina’s election statute offers challengers a remarkably low bar to question a candidate’s constitutional qualifications for office. Once someone establishes a “reasonable suspicion or belief” that a candidate is not qualified, the burden shifts to the officeseeker to prove otherwise.

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.

If nothing else, the lawyers, including two former justices of the North Carolina Supreme Court, want to depose Mr. Cawthorn as part of discovery to question his actions before, during and after the attack on the Capitol.