TRYING TO UNDERSTAND JOE…. There’s some question about what Joe Lieberman told Harry Reid about the Senate health care compromise last week. Aides say the Connecticut senator signaled his support for a Medicare buy-in; Lieberman’s office denies it.

Whatever. We know that 10 years ago, Lieberman sought national office and heartily endorsed a Medicare buy-in. We know that as recently as three months ago, Lieberman supported a Medicare buy-in. We know that as recently as six days ago, Lieberman was at least open to trading the public option for a Medicare buy-in.

And we know that as of yesterday, Lieberman has discovered that he’s so opposed to a Medicare buy-in that he’ll kill the entre health care reform effort if it stays in the bill.

There’s been ample speculation about what motivates Lieberman, and what compels him to be so profoundly annoying. My hunch is that the independent senator is just spiteful, and wants to deny the left any victory at all. But Jon Chait offers an argument I haven’t seen emphasized elsewhere: maybe Joe Lieberman just isn’t very bright.

I also think liberals, myself included, might be driving ourselves a little nuts trying to divine Lieberman’s motives. He keeps flip-flopping and explaining his shifts by making demonstrably false claims. What’s his game? Why does he keep saying these wrong, uninformed things?

I think one answer here is that Lieberman isn’t actually all that smart. He speaks, and seems to think, exclusively in terms of generalities and broad statements of principle. But there’s little evidence that he’s a sharp or clear thinker, and certainly no evidence that he knows or cares about the details of health care reform. At one point during the 2000 recount, the Gore campaign explained to Lieberman why lowering standards for military ballots would be totally unfair and illegal, and Lieberman proceeded to go on television and subvert the campaign’s position. Gore loyalists interpreted this as a sellout, but perhaps the more plausible explanation was that Lieberman — who, after all, badly wanted to be vice-President — just didn’t understand the details of the Gore position well enough to defend it. The guy was taken apart by Dick Cheney in the 2000 veep debate. […]

I think he just has no idea what he’s talking about and doesn’t care to learn.

This seems entirely plausible, and would explain quite a bit. But let’s not forget that the measures are not mutually exclusive — Lieberman can be a petty ideologue and a dimwitted annoyance at the same time.

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Steve Benen

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.