Joe Lieberman's office is right around the corner from Barack Obama's in the modernistic Hart Senate Office Building on Capitol Hill. Obama isn't around much these days, he's out campaigning. Still, the tourists show up. Lieberman can see them posing for pictures by the name plate outside Obama's office.

Lieberman would never admit it, but it must irk him the way Obama is celebrated as a politician for the post-partisan age while Lieberman himself is scorned by Democrats for adding the 'Independent' label to his Democratic Party registration. In the partisan skirmishes that dictate today's politics, Lieberman is in limbo. Neither side fully trusts him, though his standing among Republicans is higher because of his support for the Iraq War, a position that colors their view of him in a positive way, just as it turns off Democrats.

Lieberman's best friends in the Senate are Republicans John McCain, a soul mate on Iraq, and Susan Collins, a Maine moderate and the ranking Republican on the Government Reform Committee Lieberman chairs. Collins is up for re-election in '08, and Lieberman doesn't care that she has an R after her name; he's endorsing her. They've joined forces on a number of issues and are each other's biggest fans. Lieberman doesn't feel obliged to do the Democratic Party's business and help knock off Collins. She's in a tough race, straddling opposition to the war with loyalty to the president, and she's at the top of the Democrats' target list. Another politician in a similar bind of conflicting loyalty might choose to stay neutral, but Lieberman is upfront with his support, a sign of good character to Republicans, evidence he's written himself out of the party to Democrats.

If John McCain manages to resuscitate his campaign and win his party's nomination, Lieberman would almost certainly endorse him. They've partnered on Iraq and combating global warming, all the tough stuff, and Lieberman sees himself in the same mold as McCain, challenging party orthodoxy to do the right thing. Lieberman has not shown his hand as to who else among the Republicans he might be inclined to support, but he knows Rudy Giuliani and he did committee work in the Senate with Fred Thompson. On the Democratic side, he likes Obama, but it's hard to see him lining up with Hillary Clinton. Despite all the surface bonhomie he exudes as a politician, Lieberman is good at carrying grudges. He'll never forgive Hillary for backing antiwar Democrat Ned Lamont against him in the '06 Senate race. Hillary and other national Democrats did little for Lamont and Lieberman won re-election easily as an Independent, but that didn't lessen the hurt.

Lieberman is the odd man out in the Senate Democratic caucus on Iraq, but on Iran, which could be Bush's next battleground, Lieberman found plenty of Democrats willing to sign onto an amendment calling on the administration to designate Iran's Republican Guard a terrorist organization. The designation would open the door to economic sanctions, but it would also break precedent and ratchet up the war of words between Washington and Tehran. Bush hasn't settled the debate among his own advisers, and the amendment is a nonbinding "sense of the Senate" with no practical effect. Still, bellicose language added at the last minute ignited the liberal blogosphere and sent the Democratic presidential contenders running for cover with one notable exception. Hillary Clinton worked with Lieberman to take out the offensive language and replace it with language urging economic sanctions as a diplomatic tool. Then she voted for the amendment. And then she caught hell.

Call Clinton's actions calculating and compromising, but that's what presidents do, they make accommodations, they're not purists, and they balance the interests around them. A senator from New York who did not vote to condemn the country whose leader vows to wipe Israel from the map would not be long for this political world. Obama missed the vote, but said he would have voted no if he had been there. That's not as damning as John Kerry's, "I voted for it before I voted against it," but it is emblematic of a campaign that floats like a butterfly but hasn't yet learned how to sting like a bee.