The basic constraint is that there are more problems in international relations than solutions. The critics I cite often rely on two fallacies: first, that Putin is driven by Obama’s weakness; second, that the seizure of Crimea is a great win for Russia.

The Soviet Union didn’t invade Hungary because of President Eisenhower’s weakness, nor Czechoslovakia because of President Johnson’s weakness. Russia didn’t help dismember Moldova because of George H.W. Bush’s weakness or invade Georgia because of George W. Bush’s.

We don’t have much leverage because Putin cares far more about Ukraine than he does about being in the G-8. So, by all means, let’s raise the cost of aggression with banking sanctions (which proved most effective against North Korea and Iran), but let’s also recognize that, in the long run, it’s Putin who has stumbled here.

Russia has just driven Ukraine into the West’s orbit and acquired a long-term headache. Russia is already pouring billions of dollars into the bits of Georgia and Moldova that it pilfered, and now it’ll have to subsidize Crimea (which depends on Ukraine for water and electricity).