The US has taken its lumps, and rightfully so, on may occasions when it has meddled in the affairs of other nations. However, this is a case of "meddling" This is a case of intervening on behalf of a country that has asked the US to do so in no uncertain terms to help it fend of an invasion by a neighboring country that is ruled by a psychopath.
The US can and should intervene here. In 1939 when one country ruled by a psychopath invaded a neighboring country it precipitated a war killing 70 million people. Stop Putin here in Ukraine, and like any bully given a bloody nose, he'll think twice before he tries to push around another neighbor. Don't stop him here and he's only encouraged.