(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.
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Frida Ghitis: What will President Obama do about the Ukraine crisis?
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Ghitis: He has four options, like stop making empty threats toward Russia
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She says U.S. should impose real sanctions or else it looks like paper tiger
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Ghitis: U.S. military intervention is slim; Obama could turn his back on Ukraine
With the crisis continuing to escalate, @placeholder can choose between four courses of action.