RALEIGH, N.C. — [Read more about fake ballots, mail-in voting and voter fraud.]

Republican politicians across the country have for years railed against the threat of voter fraud. Some have made unproven claims about how rampant it has become in order to pass voter ID laws and open sweeping investigations. The sanctity of the vote, they have said, must be protected at all costs.

But when a hard-fought congressional election in North Carolina — in which a Republican candidate appeared to narrowly beat his Democratic opponent — was overturned this week because of election fraud by a Republican political operative, the party was measured, and largely muted, in its response.

The state party chairman, Robin Hayes, issued a statement after officials ordered a new election calling the affair “a tremendously difficult situation for all involved.” National Republicans have been mostly mum. President Trump, who has made election fraud one of the hallmarks of his administration, was quiet on Twitter, although on Friday, facing reporters at the Oval Office, he condemned fraud — “all of it, and that includes North Carolina.”

Mark Harris, the Republican nominee, had eked out a 905-vote lead over Dan McCready. But the North Carolina Board of Elections refused to certify Mr. Harris as the winner and opened an investigation into irregularities. This week, the five-member board, made up of Republicans and Democrats, convened an evidentiary hearing in Raleigh at which witnesses described a voter-turnout effort that relied on the rogue collection of absentee ballots.