The U.S. Constitution doesn’t allow states to invent qualifications for serving in Congress and exclude candidates from the ballot for failing to meet them. Yet that is precisely what the North Carolina State Board of Elections is trying to do to Rep. Madison Cawthorn.

Mr. Cawthorn, who was elected in 2020, attended President Trump’s rally in Washington on Jan. 6, 2021. Mr. Cawthorn offered acerbic rhetoric ahead of and during the rally, falsely casting doubt on the election result and using the word “fight” when addressing...

GOP Rep. Madison Cawthorn waits ahead of a visit from former U.S. President Donald Trump and Texas Governor Greg Abbott in Pharr, Texas, June 30, 2021.

Photo: callaghan o'hare/Reuters

The U.S. Constitution doesn’t allow states to invent qualifications for serving in Congress and exclude candidates from the ballot for failing to meet them. Yet that is precisely what the North Carolina State Board of Elections is trying to do to Rep. Madison Cawthorn.

Mr. Cawthorn, who was elected in 2020, attended President Trump’s rally in Washington on Jan. 6, 2021. Mr. Cawthorn offered acerbic rhetoric ahead of and during the rally, falsely casting doubt on the election result and using the word “fight” when addressing the audience. Senate Minority Leader Mitch McConnell called the riot that ensued at the Capitol a “failed insurrection.”

Opponents of Mr. Cawthorn argue that he is ineligible to serve in Congress, despite his current service there. They point to Section 3 of the 14th Amendment, a provision enacted after the Civil War, which says that no one may be a member of Congress who has taken an oath to support the Constitution and later “engaged in insurrection or rebellion” against the U.S.

But who decides whether Mr. Cawthorn is eligible? In North Carolina, the five-member state election board is empowered to hear challenges to candidates’ eligibility. The board can hold a hearing, take evidence and issue a judgment. If it concludes that a candidate is ineligible, the board can exclude him from the ballot. Excluded candidates can appeal that decision in court.

A group of North Carolina voters challenged Mr. Cawthorn’s eligibility. That process is on hold while state courts hear redistricting cases, but Mr. Cawthorn has filed a federal lawsuit arguing that the board lacks the power to review his qualifications.

It would be unconstitutional if the board attempted to take Mr. Cawthorn off the ballot. In 1995 the Supreme Court held in U.S. Term Limits Inc. v. Thornton that a term-limits amendment in Arkansas couldn’t apply to congressional candidates. The qualifications enumerated in the Constitution, the court explained, are “fixed and exclusive.” When a state tries to enforce an existing constitutional qualification, it may believe it is acting appropriately, but when it does so months ahead of Election Day, it often adds a qualification that the Constitution forbids.

In 2014 opponents of Sen. Mary Landrieu’s candidacy tried to keep her off the Louisiana ballot. They argued she had moved to Washington and was no longer an inhabitant of Louisiana and constitutionally ineligible. A state court rightly tossed out the challenge, saying she didn’t need to prove where she lived before the election.

Even if Mr. Cawthorn were an “insurrectionist”—a matter of legal and factual debate—it wouldn’t be a permanent bar to holding office. The Constitution provides that “Congress may by a vote of two-thirds of each House, remove such disability.” We don’t know whether Congress will decide before Election Day to bar from the House all who were involved in the events of Jan. 6 riot, but the Constitution is clear: The decision isn’t North Carolina’s to make.

States can’t review a candidate’s qualifications because the Constitution reserves that power to Congress itself. If voters elect a rascal who is constitutionally ineligible to serve, the people’s representatives must decide whether or not to throw him out of the House.

Mr. Muller is a law professor at the University of Iowa.

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