The only reasonable response, then, must be a powerful diplomatic thrust to isolate Putin and make immediately clear the costs of moving beyond Crimea into the rest of Ukraine. The risks for Obama in this are huge but he has no choice but to take them. Despite the fact that he needs the good will of Moscow in order to resolve the nuclear talks with Iran and peace negotiations over Syria, Obama must gamble that if he leads a decisive, united world response to the Crimean incursion, it will at once impress the Russian president and make Putin worry about his and Russia’s international image, a concern of the Kremlin’s that was so obvious during the just-concluded Sochi Olympics. Putin must be made to calculate that further recalcitrance not only over Ukraine but over Iran and Syria as well will only isolate him further…

At the same time, the United States and Europe should immediately agree to a massive economic aid package for Ukraine. The protests in Kiev that began last year were touched off by Ukraine’s economic straits and the question of whether membership in the European Union was forthcoming, and a show of economic force now will speak louder than an army. These responses should not be dragged out, not with Putin and the Ukrainians hanging on Obama’s every move. “Time is important,” says Burns. “Symbolism is going to be important.” In other words, the last thing Obama should be doing now is convening a months-long policy review as he did with Afghanistan or Syria.

Another step Obama could take is to call for a vote in the UN Security Council calling on Moscow to rescind the authorization to use force. As former NATO ambassador Ivo Daalder puts it, “Russia will of course veto such a resolution, but it will be important for the other members (including China, which staunchly opposes such interference in internal affairs of another state) to stand together against Russia.” In addition, even though NATO is not obligated to defend Ukraine, it should be called upon to deliver a strong statement reiterating its public support for Ukraine’s independence and sovereignty.