Intellectually, Rubio’s answer was pitiful. ISIS has been around since he launched his presidential campaign, but only now, with Trump and Cruz beating him in the polls, is he using it as an excuse to restrict legal immigration. Nor did ISIS invent the possibility that jihadist terrorists might get visas. All 19 men who brought down the Twin Towers entered the United States legally. In reality, Rubio’s answer has nothing do with ISIS and everything to do with the fact that, having planned to run as the man who could help Republicans embrace multicultural America, he now realizes that most of them want to build a wall to keep it.

So, Rubio, belatedly, is trying to be their man. The contrast with Jeb Bush is striking. For months now, Bush has been Trump’s punching bag. His inability to convert his vast fundraising haul into voter support has made him a political laughingstock. Yet on the stage in North Charleston, Bush showed some decency, maybe even courage. Asked about Trump’s plan to impose a religious test on entering the country, he warned that, “You cannot make rash statements and expect the rest of the world to respond as though, well, it’s just politics. Every time we send signals like this, we send a signal of weakness, not strength.”

But for Rubio, it is just politics.