U.S. District Judge Richard E. Myers II, an appointee of President Donald J. Trump, stepped in to squelch an effort by lawyers and voters in North Carolina who had filed a motion before the state’s Board of Elections declaring Mr. Cawthorn, 26, ineligible for re-election under the Constitution. They had contended that the first-term Republican’s support for rioters who attacked the Capitol on Jan. 6, 2021, made him an “insurrectionist,” and therefore barred him from office under the little-known third section of the 14th Amendment, adopted during Reconstruction to punish members of the Confederacy.

That section declares that “no person shall” hold “any office, civil or military, under the United States, or under any state, who, having previously taken an oath” to “support the Constitution,” had then “engaged in insurrection or rebellion against the same, or given aid or comfort to the enemies thereof.”

Judge Myers sided with the argument of James Bopp Jr., a prominent conservative campaign lawyer, who noted that section three concluded with a caveat: “Congress may by a vote of two-thirds of each House, remove such disability.” The Amnesty Act of 1872 did just that when it declared that “all political disabilities imposed by the third section” of the 14th amendment were “hereby removed from all persons whomsoever.”