In 2006 incumbent Connecticut Senator—and former Vice Presidential candidate—Joe Lieberman lost in the Democratic primaries to Ned Lamont, a relative unknown who had challenged Lieberman's support of the Patriot Act and the Iraq war. Unwilling to accept the results, Lieberman ran in the general election as an independent against his old party's own candidate, explaining that he was doing so not out of personal ambition but out of loyalty to his state, to his country, and—implausibly—to the Democratic Party. He managed to win re-election to the Senate in spite of the fact that almost twice as many Democrats voted for Lamont, mostly because—with the support of Rush Limbaugh, Sean Hannity, and Glenn Beck—he was able to get 70% of the state's Republican vote.

Although Joe Lieberman continued to caucus with the Senate Democrats, he campaigned for Sen. John McCain (R-AZ) in last year's presidential elections and even spoke at the Republican National Convention. And this week Lieberman told ABC news that he would support some Republican candidates for Congress in 2010. In spite of all this, the Senate Democratic Caucus agreed to allow him to continue on as chair of the Committee on Homeland Security and Governmental Affairs.

Now Joe Lieberman has threatened not only to vote against the Democrats health care reform package, but also to support a Republican filibuster of it. As Nate Silver says, this is tantamount to electoral suicide. As it is, a Daily Kos poll found Ned Lamont would beat him soundly if the 2006 election were held again today. And another recent poll shows that fully 64% of Connecticut voters support a public option. Opposing the Democrats' health care plan would practically guarantee a serious challenger in the 2012 election, prompting Stephen Colbert to joke that Lieberman won't "let the voters push him around."

But as Maura Keaney points out, Lieberman's opposition to the health care package stands to benefit Connecticut's powerful health insurance industry. He has also received more than $1,000,000 in donations from the health insurance lobby—and, of course, his wife Hadassah is a senior counselor in a public relations company's health and pharmaceutical practice. Timothy Noah likewise accuses Lieberman of a being a pawn of the insurance industry.

Progressive groups like Credo Action have already renewed their call to have Lieberman stripped of his committee chairmanship. Although the Democratic leadership have been reluctant to punish him for allying himself with Republicans. But if they really do want to pass a real health care bill, they will have to show that there is a cost to working to block their legislation.