Napoleon is said to have cautioned during an 1805 battle: “When the enemy is making a false movement we must take good care not to interrupt him.” The citation is also sometimes rendered as “Never interrupt your enemy when he is making a mistake.” Whatever the precise wording, the admonition is a useful starting point for thinking about the Ukraine situation.

Vladimir Putin has made a mistake invading Crimea, escalating a crisis for Russia that has been brewing for many months. It might have been beneficial if President Obama could have dissuaded him from this error. But Putin’s move into Crimea appeared to spring from a deeper misjudgment about the reversibility of the process that led to the breakup of Soviet Union in 1991. The further Russia wades into this revanchist strategy, the worse its troubles will become.

The Russian leader’s nostalgia for the past was on display at the Sochi Olympics. As David Remnick wrote last week in the New Yorker, Putin regards the fall of the Soviet Union as a “tragic error,” and the Olympics celebrated his vision that a strong Russia is back. That attitude led Putin to what Secretary of State John Kerry described on Sunday as a “brazen act of aggression” and a “violation of international obligations.”

Kerry called on Putin to “undo this act of invasion.” The Russian leader would save himself immense grief by following Kerry’s advice, but that seems unlikely. His mistake in Sevastopol may lead to others elsewhere, though hopefully Putin will avoid reckless actions. But the more Putin seeks to assert Russia’s strength, he will actually underline its weakness.

Perhaps inevitably, given Washington’s political monomania, the big subject over the weekend wasn’t Putin’s criminal attack on Crimea but whether Obama had encouraged it by being insufficiently muscular. There are many valid criticisms to be made of Obama’s foreign policy, especially in Syria, but the notion that Putin’s attack is somehow the United States’ fault is perverse.

For two months the Obama administration has been prodding the European Union to take the Ukraine crisis more seriously. I’m told that U.S. reporting showed that Putin was impatient with Ukraine’s pro-Russian president, Viktor Yanukovych, and wanted him to crack down even harder on the protesters in Kiev’s Maidan Square. Putin’s distaste for Yanukovych has been obvious since he fled the capital a week ago.

What Putin misunderstands most is that the center of gravity for the former Soviet Union has shifted west. Former Soviet satellites such as Poland and the Czech Republic are prosperous members of the E.U. The nations that made up what was once Yugoslavia have survived their bloody breakup, and most have emerged as strong democracies. Ukraine was set to join this movement toward the European Union last November when Yanukovych suddenly suspended trade and financial talks with the E.U. and accepted what amounted to a $15 billion bribe from Putin to stay in Russia’s camp. To the tens of thousands of courageous Ukrainians who braved the cold and police brutality to protest, Yanukovych’s submission to Moscow looked like an attempt to reverse history.

The opportunity for Putin is almost precisely opposite his atavistic vision of restoration. It is only by moving west, toward Europe, that Russia itself can reverse its demographic and political trap. Year by year, the Russian political system becomes more of a corrupt Oriental despotism — with Moscow closer to Almaty than Berlin. The alternative is for Ukraine to pull Russia with it toward the West.

As former national security adviser Zbigniew Brzezinski explained in a 2008 book, “If Ukraine moves to the West, first to the EU and eventually to NATO, the probability that Russia will move toward Europe is far greater. . . . Russians will eventually say, ‘Our future will be safest, our control over the Far East territories most assured . . . if there is a kind of Atlantic community that stretches from Lisbon to Vladivostok.’ ”

Putin’s Russia may well make more mistakes: We may see a cascading chain of error that brings Russian troops deeper into Ukraine and sets the stage for civil war. Those are the kind of miscalculations that lead to catastrophic consequences, and Obama would be wise to seek to deter Russian aggression without specifying too clearly what the U.S. ladder of escalation might be.

But Americans and Europeans should agree that this is a story about Putin’s violation of the international order. I’d be happy if we could interrupt Russia’s mistakes, but so far Putin insists on doing the wrong thing.

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