While a full-fledged military intervention and subsequent engagement with Russian troops in Crimea is obviously an absurd and horrible idea, there are reasonable steps that can be taken to ensure that Putin's actions do not go unpunished and, ultimately, to deter his further movement into Ukraine. This would include broadening sanctions against higher level Russian officials, and possibly even offering military support and capacities to Ukraine.
The United States has intervened too much with the world already, and instead of making their intervention worthwhile, they make it a costly war that gives the people worse conditions than before... Remember Iraq?
Plus, the United States already has enough problems to worry about (like a gigantic debt crisis or the fact that many people are pissed at them). The world does not need policing (especially when the United States is the police man) and its empire of protectorates is large enough already... LEAVE UKRAINE AND RUSSIA ALONE THEY DO NOT NEED USA!
This sounds like a horrible idea that is going to lead us into World War 3. The US has a long history of intervening in places we have no place intervening in, and it always ends with another country that wants us dead. Intervening is a really, really bad idea.