Trump, once regarded as a political neophyte who would inevitably self-destruct, is now increasingly seen as an unstoppable force. Photograph by Scott Olson/Getty

At about eleven-thirty on Thursday night, Donald Trump stepped off a stage at the North Charleston Coliseum, in South Carolina, and posed for some pictures with his wife, Melania, his daughter Ivanka, and his sons Eric and Donald, Jr. As Trump is fond of pointing out, they make a striking family. Chances are we will be seeing more of them.

The message that came out of this, the sixth televised G.O.P. debate, was that the Republican nomination is increasingly looking like Trump’s to lose. With the possible exception of Ted Cruz and Jeb Bush, who took their shots at the billionaire from New York, the other candidates seemed to have given up any hope of standing up to him. And neither Cruz nor Bush managed to knock Trump down. Now, it appears, only the Republican voters can do that. According to the latest polls, they don’t seem to be in any rush.

After the debate finished, Ari Fleischer, George W. Bush’s former spokesman, estimated on Twitter that Trump now had a sixty per cent chance of getting the nomination. That’s just one person’s opinion, of course, but it reflects a widespread fatalism in the Republican establishment. Trump, once regarded as a political neophyte who would inevitably self-destruct, is now increasingly seen as an unstoppable force.

Cruz, who is running neck-and-neck with Trump in the Iowa polls, had a good start to the night, parrying a question about a report, in the Times, that revealed that he and his wife had taken out, and failed to disclose, a loan from Goldman Sachs to help fund his 2012 Senate campaign, during which he had portrayed himself as an enemy of Wall Street and Wall Street bailouts. In his response, Cruz described the failure to disclose the loan to the Federal Election Commission as a “paperwork error,” continuing, “If that’s the best the New York Times has got, they better go back to the well.”

Fox Business Network’s Neil Cavuto, one of the hosts, then asked Cruz about whether, having been born in Canada, he is eligible to be President. This is the so-called “birther question,” which Trump has recently raised. “You know, back in September, my friend Donald said that he had had his lawyers look at this from every which way, and there was no issue there. There was nothing to this birther issue,” Cruz replied. “Now, since September, the Constitution hasn’t changed. But the poll numbers have.”

There followed a lengthy interchange, in which Cruz displayed the verbal skills that made him a champion debater in college, and Trump was reduced to claiming he had only brought it up to spare the Republican Party the trouble of a possible court battle if the Democrats were to sue to prevent Cruz from taking office. Asked to respond to this argument, Cruz said, dismissively, “I’ve spent my entire life defending the Constitution before the U.S. Supreme Court. And I’ll tell you, I’m not going to be taking legal advice from Donald Trump.”

Cruz clearly bested Trump in this exchange. Unfortunately for him, he appeared to let it go to his head. Trump, as the boxing promoter Don King sagely noted some time ago, is a counter-puncher: if you slug him, he comes right back at you. Cruz appeared to forget this—or to ignore it. When Maria Bartiromo, the other moderator, asked Cruz about a comment he made earlier this week in which he said that Trump “embodies New York values,” he should have proceeded with caution. For days, New Yorkers of all political persuasions have been railing at Cruz’s impertinence, and it was pretty obvious that Trump would have prepared something to say about it.

Rather than disowning his words, or correcting them to make it clear that he wasn’t trying to insult millions of people, Cruz doubled down, saying “everyone understands that the values in New York City are socially liberal or pro-abortion or pro-gay-marriage, focus around money and the media.” And, he said, “Not a lot of conservatives come out of Manhattan. I’m just saying.”

At that, Trump, a man who hasn’t previously been associated with the National Review or a love of the Tridentine Mass, threw out the name of the late William F. Buckley, Jr. And he went on to deliver a little speech that is perhaps the only thing he has said in the entire campaign that is worth quoting at length. This is what he said: