Gates said he felt that Russian President Vladimir Putin would likely be able to annex Crimea, but not necessarily with military force.
"I think he does not want to send troops into Eastern Ukraine," Gates said.
The former defense secretary also defended President Obama, who's been under fire from conservatives for being too weak.
"Putin invaded Georgia when George W. Bush was president. Nobody ever accused George W. Bush of being weak or unwilling to use military force," he said. "I think Putin saw an opportunity here, and he has seized it."