Vladimir Putin’s ascent to power crushed those hopes. For a long time, however, Europeans—and Americans too—hesitated to acknowledge what was happening in Russia. There were some good reasons for this hesitation: Putin did sometimes cooperate with the Western world—in Afghanistan, for example. There were bad reasons too. As energy prices rose after 2000, the Russian economy recovered. Russia had more of value to sell to the rest of the world, and more money to buy things that the West had to sell—more money, too, to buy Western politicians.

Above all, nobody wanted to return to the days of living in a Europe armed against itself, divided into hostile blocs, with horrifying war a push of a button away. The human mind is constituted in such a way that what we don’t wish to believe, we can for a long time disbelieve. “The Cold War is over,” German chancellor Angela Merkel reproached the United States, when the NSA was caught surveilling German communications. But the NSA was surveilling precisely to monitor how deeply Russian espionage had penetrated the German state—because while the Cold War has ended, the security threat from Russia has not.

Suddenly, NATO’s role in Europe has regained relevance. Unfortunately, NATO lacks the credibility to match. The United States no longer maintains even a single tank in Europe. The European countries have allowed their defense capabilities to wither altogether. If the budget sequester remains in force, the U.S. Army's combat capabilities will be cut in half by decade’s end. Even if NATO decided that Russia’s latest actions release the West from the 1990s ban on permanent deployments in eastern Europe, what troops could it send?

We shouldn’t give up the hope that Putin will prove only an ugly detour on Russia’s route to a future as a normal, peaceful European democracy. But we shouldn’t any longer rely on that hope to guide our policy. Russia has become dangerous again. It's not as dangerous as it was, but it’s more than dangerous enough. Nearly 300 bereaved families in the Netherlands, Britain, Canada, and elsewhere have suffered what hundreds of Ukrainians have suffered since Russian sharpshooters opened fire on peacefully protesting crowds in Kyiv last winter.

And we are all more vulnerable to that danger because we have let atrophy the institutions necessary to meet and contain that danger. It’s time—past time—to build those institutions back. That’s been the meaning of the Ukraine crisis from the start. The terrible heartbreak of MH17 might have been averted if we had absorbed that meaning early. But better to absorb it now than to leave it any longer.