The boldest and riskiest course would be to dispatch 50 or 60 of the incredibly potent F-22s to Poland plus Patriot batteries and appropriate ground support and protection. Russian generals and even Putin surely know that the F-22s could smash the far inferior Russian air force and then punish Russian armies invading eastern Ukraine or elsewhere in the region.

There’s no sense at all in making this move unless Obama unambiguously resolves to use the F-22s. The worst thing to do is bluff. Nor would the dangers end there even if Obama were not bluffing; Putin might think he was bluffing anyway and start a war. With all these complications and risks, the Obama team still should give this option a serious look—and let Russia and our NATO partners know this tough course is under serious consideration. Obama has sent a few F-15’s and F-16’s to Eastern Europe, some military aid to Ukraine and other states. But everyone knows this is tokenism.

Another plausible and perhaps less risky measure: help prepare Ukrainians for guerrilla war against an invading Russian force. Pound for pound in conventional war, the Ukrainian forces are no match whatsoever for the Russians. But irregular Ukrainian troops armed with first-class rifles, mortars, and explosive devices would do Russian troops great damage. Russians know this. They have surely not forgotten the horrors fighting guerrillas in Afghanistan.