And so the main goal of the United States, the EU, and NATO should be to deter and dissuade Putin from moving his troops deeper into Ukraine. There are two ways to do this, seemingly contradictory but actually (if well-managed) complementary. First, ratchet up the penalties. Second, leave room for diplomacy.
The penalties should include—right now—stepping up military deployments to the NATO allies, especially to Poland and the Baltic nations, which were once tied to the Soviet Union. Another: Draw up plans for containing and countering Russian troops in the event of an incursion into Ukraine—not sending U.S. or NATO troops, but shipping arms, maybe some advisers and black-bag Delta forces—and talk about these plans with the allies, and Ukrainian officials, on open phone lines. Putin surely knows the limits of his army. The ground forces in that sector of Russia could invade Ukraine, but they lack the resources and logistical lines to sustain an occupation for very long, especially in the event of even slight resistance. We have to make him realize we know these limitations, too.
Over those same unencrypted phone lines, a senior official should also talk about some moves that would really isolate Russia from the rest of the world, too—cutting it off from all international forums (Putin, above all, wants to be respected as a major world figure), freezing out not just a couple dozen Kremlin cronies but Russian banks and corporations. Again, these are threats of actions to take place if Russia goes deeper into Ukraine—not reprisals for the seizure of Crimea, which would have no effect and probably wouldn’t be enforced anyway.