Two adages came to mind this week when Senate Democrats voted to let Connecticut Sen. Joe Lieberman hold onto the chairmanship of the Homeland Security Committee despite his treachery in the recent election. The first: Keep your friends close and your enemies closer. The second: Revenge is a dish best served cold.

While President-elect Barack Obama said he favored keeping Mr. Lieberman in the Democratic caucus (the better to keep an eye on him, no doubt), he took no position on the chairmanship -- and rightly so. Congress is still an independent branch of government, even if it doesn't always act like it.

Mr. Lieberman made it clear that if he lost his plum post he would bolt the caucus. Tempting as it must have been to let him stalk off into irrelevancy, most Democrats were thinking more practically. They need him for their one-vote majority in the lame duck session. More to the point, they're only two undecided races away from a theoretically filibuster-proof, 60-seat majority next year.

So while Joe the Plumber is gone from the national spotlight, Joe the Bummer is not. Still, the man would do well to watch his back. Given his recent record, it might not take much for the pack to turn against him.

The new Democratic-led government will have its hands full trying to reassemble the Constitution that Mr. Lieberman (and others) helped Republicans shred, and to extract the nation from a wrong-headed war for which he was a major cheerleader. So, in the new world order, Sen. Bummer will have to get busy undoing some of his own damage. That, in itself, could be worth the irritation of keeping him around. But as the Bush era ends and Senate Democrats shake off the Stockholm syndrome (in which hostages identify with their captors), they might not take kindly to Mr. Lieberman committing any new transgressions.

Of course, he wasn't the only Democratic lawmaker to climb on the Bush/Cheney Express after the 9/11 attacks. If anything, he was squarely in the majority -- the most notable exception being the president-elect. But Mr. Lieberman is the only one to have compounded his sins by stumping on the campaign trail proudly, even gleefully, for the other side.

His colleagues could have stripped him of his chairmanship as punishment and it would have been richly deserved. In fact, they could have done so simply because they were tired of listening to him whine. Instead, they kicked him off the Environment and Public Works Committee, on which he had sat for 20 years. The next day, Sen. Bummer was shamelessly spinning even that slap on the wrist as a voluntary relinquishment and a good-will gesture on his part. So much for being chastened.

Keep in mind that Mr. Lieberman didn't just support his good buddy John McCain's quest for the presidency. He also delivered a prime-time endorsement at the Republican National Convention and, on several occasions, made harsh comments about the Democratic nominee. Worse, he deliberately twisted Mr. Obama's vote against indefinite funding for the Iraq war, mischaracterizing it as a vote to cut off support for troops currently engaged in battle.

OK, so people say harsh things in the heat of a campaign, and Mr. Lieberman has now said he wishes he hadn't uttered some of the things he did. But he didn't just pop off in front of a microphone. He also supported another good buddy, Sen. Norm Coleman, R- Minnesota, against Democratic challenger Al Franken, and the two are now locked in a bitter recount. Mr. Franken is one of two remaining keys to that 60-seat majority. If he loses, the golden ring will be out of reach, and Senate Dems who were singing "Kumbaya" this week may change their tune to "The Backstabbers."

There's little doubt that Mr. Lieberman's behavior was partly motivated by the same desire for retribution that his colleagues have so far declined to pursue against him. Even though the party supported him as Al Gore's running mate in 2000, any appreciation for the honor was wiped out after he lost the 2006 Senate primary in Connecticut, mostly because of his hawkishness on the Iraq war.

He ran anyway, as an Independent. At that point, Democrats such as Hillary Clinton who'd backed him in the primary switched their support to the party's nominee. Mr. Lieberman won anyway, by raking in Republican votes. He continued to caucus with the Democrats but never forgave them, and the next election cycle presented the perfect opportunity for payback. Now he is benefiting from a forgive-and-move-on attitude that he himself did not see fit to display.

Spitting on the party that so recently backed you for the second-highest office in the land would normally have severe consequences, but this not a normal election year. In the midst of the worst financial crack-up since the Great Depression, the nation has enormous problems to solve and very little money with which to solve them. It is also about to hand the reins of power to a man who values solutions over ideology and who wants all hands on deck to repair the damage of the past eight years.

In that context -- and keeping in mind Yitzhak Rabin's wise observation that you can't make peace with your friends -- there is something to be said for putting personal grievances aside and getting down to work. Perhaps it's fitting that the first beneficiary of that no-grudge policy is the person who least deserves it. But he still better watch his back.