Obama's only mistake on Ukraine was suggesting that there would be consequences

Under such circumstances in a crisis of this potential magnitude, Obama should be looking for common interests. One such interest is ending the bloodshed. Even Putin couldn’t want to send troops to the Ukrainian heartland. The Russian army is hardly in tip-top shape: It could probably mount an invasion, but who knows how long it could sustain an occupation, especially in the face of nationalist insurgents who have a fierce, even ancestral hatred of Russia.

Perhaps Obama could offer assurances that he won’t offer Ukraine membership in NATO (that’s not a live issue anyway), nor will he push to revive the plan for Ukraine to join the European Union. This latter pledge would be a big deal: The protests were set off when Yanukovich cancelled plans for a formal association with the EU, after Putin lured him back into Moscow’s bed with a $15 billion aid program. In exchange for these assurances, Putin would call off his shock troops, recognize the Ukrainian parliament’s ouster of Yanukovich (whom Putin never liked anyway), and allow Ukrainian elections to go ahead this May, perhaps under international observation. Obama could present the deal as a victory for democracy (the Ukrainian people will decide!). Putin could swallow the deal, believing that a pro-Russia candidate might win (legitimately or otherwise). In any event, the Ukrainian politicians will have been shown what Putin could do if they get out in front of their skis again.