Putin knows that. He also figured out somewhere, probably at a G-8 that Obama is a rookie, incompetent and a blow hard. Putin did not survive he KGB, Russian politics and two terms by being a wuss and he sure has the ability to take the measure of a man. So is he ready to have one dropped on Moscow for the sake of Ukraine?
Under Obama, he knows that won't ever happen, the the "Oh!" will offer cash instead. Aid if you get out or something.
Under Reagan? Bush 41? Clinton? Bush 43?
He's in there because he looked into Obama's eyes one time and knew he could.