On most issues Donald Trump is inconstant, persuadable, bored and eager to move on. But on a few questions there is real consistency across his years as a public eminence. One is his belief, which may give us new steel tariffs, that America is a big loser from the international trade system. Another, which may give us a Trumpian tête-à-tête with Kim Jong-un, is his belief that he alone can solve the problem of nuclear proliferation.

In 1984, near the peak of Reagan-era nuclear fears, he told The Washington Post that he should lead nuclear deal-making with the Soviets. Six years later, he warned Playboy that “the greatest of all stupidities is people’s believing [nuclear war] will never happen.” In 1999, flirting with a presidential bid, he promised to “negotiate like crazy” to prevent North Korea from going nuclear.

Now he gets the chance to actually follow through on these boasts (though the chances of a Kim-Trump summit actually coming off are perhaps still somewhat modest). And as with many problems to which Trump is getting the chance to turn his hand, one can doubt his competence and judgment while also doubting the perfect wisdom of the approaches that preceded him.

The dilemma facing American policymakers since the Cold War is that you can have a denuclearizing world or you can have a world where liberal values are always on the march — but you can’t necessarily have both. We have failed to strike a lasting deal with the North Koreans because they are duplicitous and wicked, certainly. But we also have no clear example to offer Pyongyang of a denuclearization that worked out for the authoritarian regime that accepted it.