Back in the 1950s, when the institutions were still new and shaky, I’m sure many people feared the Western alliance might never take off. Perhaps in the 1970s, the era of the Red Brigades and Vietnam, many more feared that the West would not survive. But in my adult life, I cannot remember a moment as dramatic as this: Right now, we are two or three bad elections away from the end of NATO, the end of the European Union and maybe the end of the liberal world order as we know it.

In the United States, we are faced with the real possibility of Republican Party presidential nominee Donald Trump, which means we have to take seriously the possibility of a President Trump. Hillary Clinton’s campaign might implode for any number of reasons, too obvious to rehash here; elections are funny things, and electorates are fickle. That means that next January we could have, in the White House, a man who is totally uninterested in what presidents Obama, Bush, Clinton, Reagan — as well as Johnson, Nixon and Truman — would all have called “our shared values.”

Trump has advocated torture, mass deportation, religious discrimination. He brags that he “would not care that much” whether Ukraine were admitted to NATO; he has no interest in NATO and its security guarantees. Of Europe, he has written that “their conflicts are not worth American lives. Pulling back from Europe would save this country millions of dollars annually.” In any case, he prefers the company of dictators to that of other democrats. “You can make deals with those people,” he said of Russia. “I would have a great relationship with [Vladimir] Putin.” 

Not only is Trump uninterested in America’s alliances, he would be incapable of sustaining them. In practice, both military and economic unions require not the skills of a shady property magnate who “makes deals” but boring negotiations, unsatisfying compromises and, sometimes, the sacrifice of one’s own national preferences for the greater good. In an era when foreign policy debate has in most Western countries disappeared altogether, replaced by the reality TV of political entertainment, all of these things are much harder to explain and justify to a public that isn’t remotely interested.

And Americans aren’t the only ones who find their alliances burdensome. A year from now, France also holds a presidential election. One of the front-runners, Marine Le Pen of the National Front, has promised to leave both NATO and the E.U. , to nationalize French companies and to restrict foreign investors. Like Trump, she foresees a special relationship with Russia, whose banks are funding her election campaign. French friends assure me that if she makes it to the final round, the center-left and center-right will band together, as they did two decades ago against her father. But elections are funny things, and electorates are fickle. What if Le Pen’s opponent suddenly falls victim to a scandal? What if another Islamic State attack jolts Paris? ...