Principles, reflected in an intolerance for rotten behavior in your own ranks. That's the nice answer--the noble removing the less noble from their presence.

The answer from my cynical side is the Republican terror of a media almost totally united and aligned with the Democratic Party, and able to crucify any one of them at will. That's the less nice answer--throwing one of your own to the ravening wolves to save your own sorry ass.

I'm not sure how cynical I'm feeling today.

Maybe the question you should be asking is how come Democrats and their alllies will defend corrupt lying bastards like Clinton, Torricelli, Kennedy and others, down to the last extreme, just so they can remain in power?