Call it President Trump’s Reykjavik moment. He canceled the Singapore summit with the North Korean communist party boss, Kim Jong Un, the way President Reagan walked out on the Soviets at Reykjavik. The minute the North Koreans issued a statement calling Vice President Pence “stupid,” it was time to kaput the parley. No president could stand for his vice president to be spoken of that way. We have little doubt that most Americans will back Mr. Trump.

Of course, the liberals are going to blame Mr. Trump (as the liberals blamed Reagan). The Times’ Nicholas Kristof was the first to get into pixels with that line today. He worries that we’re entering a “more dangerous” patch and avers that Mr. Trump’s decision to cancel “topped a particularly inept diplomatic period.” The old policy of “maximum economic pressure on North Korea,” he reckons, “may no longer be viable.”

“As every president since Nixon — except for Trump — has realized, the military options are too dangerous to employ,” writes Mr. Kristof, whom we admire as an intrepid reporter who’s made at least two reporting trips to Pyongyang. Of the military option being too dangerous, he writes: “That’s even more true today, when North Korea apparently has the capacity to use nuclear, chemical and biological weapons against Seoul, Tokyo and perhaps Los Angeles.”

It happens that the editor of the Sun was editing the Forward when, back in 1994, it argued for a preemptive strike against North Korea. He has told those who pull the editorial oars in this galley that he doesn’t remember Mr. Kristof or the Times ever pitching in during the argument for preemption. To suggest a generation later that the military option might once have been viable, well, where were they when they thought it was?

History is incredibly stubborn in her refusal to disclose her alternatives. So let’s focus on the future. The collapse of the Singapore summit is an opportunity for a public airing of what, if anything, we want from North Korea in the first place. Our own opposition to the Singapore summit arose from a sense that we were readying a security guarantee for North Korea and Mr. Kim himself. What in the world is the logic of that?

More than 33,000 American men fell for freedom in Korea. What is the basis now to cut a deal that would have us guarantee the future of the North Korean communist regime? It is well to recall the panic on the left when President Reagan walked out of Reykjavik. He himself was down about it, as Donald Regan, his staff chief, recalled from their ride together for his plane back to Washington. Yet Reagan’s stand for principle lead instead to victory in the Cold War.

Mr. Trump has a source of confidence Mr. Kim lacks — political legitimacy. Mr. Kim lost his cool because he knows that he has no democratic standing. He rules by tyranny. He fears the Libyan model mentioned by Mr. Pence not because Libya gave up its nuclear program but because in the end, Libya’s dictator, Colonel Gadhafi, was dragged from a culvert and shot to death by his own people. Mr. Kim must lie awake at night worrying about such a fate.