A MAN OF (MEANINGLESS AND SHALLOW) PRINCIPLES…. John McCain had a tweet today that’s made the rounds.

Joe Lieberman — standing up for his principles on health care is being viciously attacked by the liberal left…what a disgrace!

Now, considering the source, this isn’t much of an insult. After his conduct of the last few years, John McCain knows all about what constitutes a “disgrace.”

For that matter, I’m not sure what the “liberal left” is supposed to do right now to meet with McCain’s approval. Joe Lieberman has decided to kneecap health care reform just feet from the finish line, and the “liberal left” is pointing out the absurdities of the senator’s behavior. McCain has quite a bit of experience with vicious attacks, but criticizing Lieberman’s betrayal is hardly beyond the pale.

But the part of McCain’s remark that stood out for me is the notion that Lieberman is “standing up for his principles.” Really? What principles would those be? The principle that allows an experienced senator to kill a bill over a provision that he publicly endorsed just three months ago?

If Lieberman was acting on principle, I’d be more inclined to respect his opposition. But therein lies the point: there’s no coherence, better yet principle, to rationalize Lieberman’s behavior.

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Follow Steve on Twitter @stevebenen. Steve Benen is a producer at MSNBC's The Rachel Maddow Show. He was the principal contributor to the Washington Monthly's Political Animal blog from August 2008 until January 2012.