Brooks also argues that:

There’s a theory going around that Lieberman was embittered by the trauma of 2006 when Democratic primary voters in Connecticut defeated him because of his support for the Iraq war. There’s little evidence to validate this.

Meanwhile, back on Planet Earth, Lieberman was the instrument that finished the public option. After years of favoring one.

And why did Lieberman oppose a public option? Because "liberal" activists were in favor:

For close to a decade, he got nearly perfect scores from the American Public Health Association, which backs a single-payer health-care system, and in lieu of that, the “public option.” Now, all of a sudden, he’s so outraged by a public option that he’s threatening to filibuster any bill that contains it. The arguments he makes on behalf of his new position are remarkably weak: He says the public option will raise costs, even though the Congressional Budget Office has said no such thing, and even though logic suggests that by competing with private insurers, a government plan will actually drive costs down. Some have accused Lieberman of shifting right in order to win backing from the insurance industry in preparation for a 2012 reelection run. But, in fact, he gets relatively little insurance money, and Connecticut politicos mostly think he won’t run.

So why is he doing this? Because he’s bitter. According to former staffers and associates, he was upset by his dismal showing in the 2004 Democratic presidential primary. And he was enraged by the tepid support he got from many party leaders in 2006, when he lost the Democratic primary to an anti-war activist and won reelection as an independent. Gradually, this personal alienation has eaten away at his liberal domestic views. His staff has grown markedly more conservative in recent years, and his closest friends in Congress are now Republicans John McCain and Lindsey Graham. For Lieberman, the personal has become political, and it has pushed him further to the right.

Joe Lieberman ranks with the most despicable of public figures in the United States in the last decade.

Speaking for me only