That’s short term thinking. Hitler thought the same regarding the Sudentenland.
Ukraine is presently an independent nation. Putin steps in it and he will in time regret it.
We’re currently not in a position to go toe to toe with another nuclear weapon equipped country. We have weak leadership, and putin knows it, and he is exploiting it for all he can, and he will get away with it. These are the things that come to be in obama’s post american world. The US government is more worried about internal revolution than they are external threats.