"We are actively evaluating what is happening in eastern Ukraine, what actions Russia has taken, what transgressions they've engaged in," White House spokesman Jay Carney said Monday. "And we are working with our partners and assessing for ourselves what response we may choose."
As with the situation in Syria, Obama faces few good options as he watches Russia destabilize Ukraine, the former Soviet republic that has sought greater ties with Europe.
There's little appetite in either the U.S. or Europe for direct military action, and the White House said Monday it was not actively considering sending Ukraine lethal assistance. That's left Obama and his international partners largely reliant on economic and diplomatic retaliation.
The president has wielded some of his available options since the situation in Ukraine devolved in late February, but those actions so far have had little success in stopping Russian advances.
Obama's initial warning that Putin would face "costs" if he pressed into Crimea was largely brushed aside by the Russian leader, who went so far as to formally annex the peninsula from Ukraine. Economic sanctions on several of Putin's closest associates followed, as did Russia's suspension from the exclusive Group of Eight economic forum, but neither appears to have discouraged Moscow from making a play for eastern Ukraine.
On Friday, the U.S. slapped sanctions on more individuals connected to the Crimea takeover, and White House officials are weighing another round of targeted penalties against additional Russian and Ukrainian citizens.
But tens of thousands of troops massed on Russia's border with eastern Ukraine, Obama is facing calls from some Republicans to take tougher action now. Tennessee Sen. Bob Corker, the top Republican on the Senate Foreign Relations Committee, sent Obama a letter over the weekend calling on the administration to immediately ratchet up economic penalties against Moscow.