Though he lost some subgroups in South Carolina—like well-educated voters, who Rubio won, and very conservative voters, who Cruz won—exit polls showed no glaring vulnerability that could undermine him. The only GOP faction that overwhelmingly views Trump as unacceptable is national party leaders and senior operatives, whose influence is diminished by the fact that they are loathed by the GOP base (a dynamic that helped give rise to Trump in the first place).

One serious knock on Trump is that his unfavorable rating is poorer than those of Cruz and Rubio. A Quinnipiac poll found his rating with Republicans at 62 percent favorable, 31 unfavorable. Cruz’s were 62 percent favorable, 23 percent favorable; Rubio’s were 64 percent favorable, 17 percent unfavorable.

Sullivan, Rubio’s campaign manager, wrote in his memo that the Floridian “has the highest favorability of anyone in the race” and has “the most room to grow.”

But for now, at least, there is scant evidence to suggest Trump’s unfavorable ratings are at a critical mass to prevent him for getting the nomination.