The great Republican wave that swept the South starting in the late 20th Century — the very wave that Lyndon Johnson predicted after signing the Civil Rights Act in 1964 — came relatively late to North Carolina.

But when it finally hit in 2013, with Republicans controlling both the legislature and the governor’s mansion for the first time since Reconstruction, it did so with breathtaking force. Led by a group of savvy, tactically skilled state lawmakers, North Carolina Republicans set out to undo decades of center-left policy enshrined by Democrats, and to remake the rules of the political game in their favor.

They engaged in gerrymandering that ensured the party a near-lock on the state legislature and lopsided control of the state’s House delegation in Congress. They paved the way for a conservative state Supreme Court that upheld a strict voter ID law. And after gaining a veto-proof majority last year, they banned most abortions after 12 weeks of pregnancy.

And while Republicans lost the governorship in 2016, they had harbored hope of winning full control of state government again this year, bringing North Carolina in alignment with most other Southern states.

Then came Mark Robinson.

Long before this week, when CNN reported that Mr. Robinson had called himself a “black NAZI!,” discussed his pornography habits and praised slavery in an adult online forum, the bellicose Republican nominee for governor (and current lieutenant governor) was polling poorly against his Democratic rival, Josh Stein.

But now more than ever, Mr. Robinson, with his antisemitic and anti-gay rhetoric and performative, polarizing brand of politics, is sending waves of anxiety through the state party.

Thank you for your patience while we verify access. If you are in Reader mode please exit and log into your Times account, or subscribe for all of The Times.

Thank you for your patience while we verify access.

Already a subscriber? Log in.

Want all of The Times? Subscribe.