( CNN ) -- The mysterious , faceless green men have entered eastern Ukraine , looking much like they did last month in Crimea before Russia sliced off and swallowed that former province of Ukraine . What will President Barack Obama do now ? Unlike Russia 's Crimea invasion , the Ukrainian government is not rolling over as readily this time , vowing not `` to let the Crimea scenario repeat . '' That is just what Russian President Vladimir Putin needs to justify an open military assault under the guise of `` protecting '' Ukraine 's ethnic Russians . The possibility that war will break out is real . U.S. officials are convinced that the disciplined militias -- who have taken over government buildings in more than half a dozen Ukrainian cities , wearing no identifying marks on their uniforms -- are Russian special forces or `` paid operatives , '' deliberately stoking unrest , not part of a spontaneous groundswell of pro-Russia sentiment . Still , America 's warnings of serious repercussions have fallen on deaf ears . With the crisis continuing to escalate , Obama can choose between four courses of action . 1 . Stop making empty threats . Obama has repeatedly warned that `` there will be costs '' if Russia takes over Ukraine 's territory . But that is exactly what Russia did . Efforts to line up European support for stern sanctions have faltered badly . The West 's growl , its bark , seems increasingly toothless . The sanctions so far are underwhelming . Washington and its friends need to impose real sanctions and offer Ukraine real support , or else America 's warnings will be meaningless . Obama and Secretary of State John Kerry still give the impression , despite ample evidence to the contrary , that they think diplomacy and reasoning can dissuade Putin from pushing ahead with his goal to dominate Ukraine , fearing that harsh sanctions will provoke him . But one way to reverse the course is to exact a harsh economic and political cost while keeping open a way for Moscow to roll back . Obama must make a decision : If the U.S. is not ready to impose muscular sanctions , it 's time to stop issuing threats . America 's `` red lines '' risk becoming an international punch line . Feeble threats against Russia 's `` incredible act of aggression '' are hurting the U.S. , making it look like a paper tiger and making its friends more vulnerable . Grave warnings of consequences without consequences do more harm than good . 2 . Decide where to build a moat . If the U.S. is not willing to take risks for the sake of Ukraine , it is time to decide what part of the map matters . After World War II , the U.S. came to a decision to reluctantly allow Soviet control of Eastern Europe while protecting the western side of the Iron Curtain . That was a cold calculation for which the people of Poland , Czechoslovakia and elsewhere paid a steep price . But it sent a clear message to Moscow to stop at the edge of that military and ideological barrier . Washington could just as coldly concede Ukraine , or part of it , to Russia and build a ( figurative ) moat around it or choose another place on the map to do that . The U.S. must decide how far is too far . It was n't Crimea . Is it eastern Ukraine , western Ukraine , Moldova , the Baltic states ? Opinion : U.S. giving Putin green light in Ukraine ? 3 . Consider military action . The chances that the U.S. will go to war over Ukraine are extremely small , but the option exists . If Russia unleashes its military power across the border , the folder marked `` military action '' will land on the table in the situation room . Wars are unpredictable and always bring unexpected consequences . Fighting on the border of the European Union will put NATO on high alert and trigger a new set of possible outcomes . If Ukraine and Russia go to war , the calculations will change drastically and dangerously . 4 . Say goodbye and good luck to Ukraine . There 's one more option for Obama . He can turn his back on Ukraine , wish it well and move on . The U.S. could make a decision that it would rather try to continue working with Putin on issues like Iran and Syria , and allow Russia to do what it wishes in `` its part '' of the world . It 's a course of action that would satisfy American isolationists , as well as those who accept Russian claims that the troubles are America and Europe 's fault . That , unfortunately , would invite even more challenges to world peace , as it would empower bullies everywhere . American policy aims , unsuccessfully , toward option No . 1 , but the threats are far ahead of the action . Several weeks ago , I suggested that there was a chance that `` when the stakes grow high enough , the U.S. and Europe may rise to the challenge . '' That may yet happen . But so far it has not . Putin 's platoons of masked green men are wreaking havoc in Ukraine , and the U.S. still has n't quite decided how it plans to respond . In the long run , Russia will suffer from the ill will it has engendered with its bullying tactics . But in the short and medium term , it is gaining ground .
Obama : What will President Obama do about the Ukraine crisis ? Ghitis : He has 4 options , like stop making empty threats toward U.S. . She says U.S. should impose real sanctions or else it looks like paper tiger . Ghitis : Ukraine military intervention is slim ; Obama could turn his back on U.S. .