You have to wonder why the Senate Democrats are keeping Sen. Joe Lieberman in the party caucus and letting him chair the Homeland Security Committee, a plumb chairmanship that I am sure many veteran Senate Democrats, who actually call themselves Democrats, would love to have.

In 2006 Sen. Joe snubbed his nose at the Connecticut Democratic Party when he refused to abide by the results of its primary. Recall that businessman Ned Lamont won the primary against Lieberman by focusing on criticism of the Iraq invasion and Sen. Lieberman's support for it.

Rather than support the nominee, Lamont, Sen. Lieberman decided to undermine him and the party by running as an independent. He went on to win the general election. Back in the Senate he took to calling himself an "Independent Democrat," unlike, apparently, all those "Dependent Democrats" who he felt were too loyal to the party.

The Dependent Democrats, however, were not about to oust him from the Senate caucus because they needed his vote to maintain their razor thin control of the Senate.

Fast forward to the 2008 election. Lieberman, four years away from having to run for re-election himself, spends months vigorously campaigning for the party nominee for president — the Republican Party nominee, that is, Sen. John McCain. He does not draw the line at pushing McCain, he is highly critical of Democrats' choice, Sen. Barack Obama.

But Obama wins and the Dependent Democrats in the Senate increase their numbers and take solid control. Surely they will send Sen. Joe packing, where he can caucus in his party of one — the ID Party.

Not so fast. Now the Democrats need his vote to reach the magic number of 60 necessary to block filibusters, giving the party the power to close debate and get legislation to a vote. Their are smiles all around. Sen. Joe is welcomed back with a pat on the back. All is forgiven.

That number 60 now looms important as the Senate Democrats work to get a health care reform bill to a vote before year's end. Lieberman's reaction? A promise to support a Republican filibuster if the Senate bill contains a public option.

If the Democrats cannot count on Sen. Joe's vote to stop a filibuster of a legacy issue for Democrats — universal health coverage — what is he doing in the caucus?

And why is he still chairing the Homeland Security Committee, which has a big hand in doling out homeland security dollars. Next week Sen. Lieberman gets more national media attention when the committee conducts hearings into the tragic murders of military personnel at Fort Hood.

Perhaps in time the Dependent Democrats may decide to end their dependency on Sen. Lieberman.