Glenn Reynolds flashes back to 1998, "when it was okay for Democrats to sound tough"; Robert Bidinotto goes back 30 years further to reference one of the few remaining who still do:

Where have you gone, Joseph Lieberman? A nation turns its lonely eyes to you...

“A lot of Democrats are essentially pacifists and somewhat isolationist,” [Lieberman told the New Yorker]. He had particular problems with Senator Edward Kennedy’s proposal to deny the President funding for a troop surge, and with an idea recently raised by the senior senator from Connecticut, Christopher Dodd, to cap the number of American soldiers in Iraq. Lieberman was not willing to say whether he would remain a Democrat if the Party cut off funding for the war. “That would be stunning to me,” he said. “And very hurtful. And I’d be deeply affected by it. Let’s put it that way.”

Lieberman’s Democratic colleagues know that if he switched parties they would lose their majority, and so they tend to indulge him, unless they are speaking to reporters off the record.

Update: Ed Morrissey reminds us that Hillary's recent "bug out in 90-days ultimatum" could be a decisive moment for Lieberman:

The worst part about it is its nakedly political purposes. Hillary has come to regret her run to the center during her Senatorial career, and now wants to suck up to the International ANSWER set that runs the Left of the Democrats. In order to establish her bona fides and compete with Barack Obama's demand for a phased withdrawal by March 2008, she just bumped the timetable up by nine months.

It's not even clear that such a demand would be Constitutional. Congress can suspend the funding for the troops, but Congress has never actually revoked an AUMF before while hostilities continued. An attempt to do so would probably meet a Presidential veto, which Congress would be unable to override. Even if it did, the White House would sue the Congress and demand a Supreme Court decision on the legality of such a move -- which would take weeks, at the least, during which our troops would find themselves in limbo. At that time, our enemies would pounce, and create a huge political firestorm over whether we should retreat under fire.

And she wants to run to fill the role of Commander-in-Chief?

Again, watch for Joe Lieberman on this issue. He has made it clear that his loyalty to the Democrats ends at a bug-out. Hillary's demand, if pushed, may change the entire calculation in the Senate and leave Harry Reid with the title of Minority Leader. The line Lieberman drew in the sand now approaches, and Hillary apparently wants to push the Democrats far past that and over a political cliff -- and take our entire efforts against terrorism with them.