Washington — North Carolina Lt. Gov. Mark Robinson, the Republican nominee for governor, posted a slew of incendiary, explicit and racist comments on a pornographic website more than a decade ago, according to a CNN investigation released Thursday that has shaken the state’s gubernatorial race.

Mr. Robinson, the Republican nominee for governor of North Carolina, vowed to stay in the race and sought to deny the report, which also said he had defended slavery in online posts years ago.

A North Carolina loss could not only foil Trump’s re-election chances, it would be a particular home-state humiliation for his two handpicked co-chairs of the Republican National Committee: Michael Whatley, who is the state’s former GOP chair, and Lara Trump, the former president’s daughter-in-law, who is a North Carolina native.