Logistics—refurbishing troops with a line of supplies—were always the Russian army’s weak point, even in the Cold War heyday; that’s still the case. Then there’s the army itself. The special forces and paratroopers are professional, but the rest of the army consists of draftees, serving one-year terms that many of them spend drunk and disorderly. If they face any resistance, whether from the Ukrainian army (a ragtag force itself) or “irregulars” (homegrown insurgents) or outside agents (a squad or two of Delta Force troops), the Russian soldiers could find themselves seriously bogged down.

Politically, Putin would find himself on very shaky ground. Already, he mustered only 10 other countries—the likes of Belarus, Cuba, North Korea, Nicaragua, Sudan, and Syria—to oppose a U.N. resolution condemning the annexation of Crimea. If he invades Ukraine, a sovereign nation with a United Nations seat, his isolation will widen and deepen politically, diplomatically, and economically.

If he crosses that line, he will also do more than anyone ever has to rouse the European nations out of their post-Cold War stupor. He can count on Britain, Germany, and France to boost their defense budgets, and in a way that confronts Russia. He can also count on the United States to station more troops, fighter jets, maybe even armored weapons in Poland and the Baltics—to hell with concerns about provocation. And he must know the lesson that other nation-states have learned in recent years: that if he prompts a conventional conflict with the United States military, he will lose badly.