Paul Krugman understands the pundit reaction to Lieberman quite well (firewall alert!):
Imagine yourself as a politician or pundit who was gung-ho about invading Iraq, and who ridiculed those who warned that the case for war was weak and that the invasion’s aftermath could easily turn ugly. Worse yet, imagine yourself as someone who remained in denial long after it all went wrong, disparaging critics as defeatists. Now denial is no longer an option; the neocon fantasy has turned into a nightmare of fire and blood. What do you do?
You could admit your error and move on — and some have. But all too many Iraq hawks have chosen, instead, to cover their tracks by trashing the war’s critics.
They say: Pay no attention to the fact that I was wrong and the critics have been completely vindicated by events — I’m “sensible,” while those people are crazy extremists. And besides, criticizing any aspect of the war encourages the terrorists.
That’s what Joe Lieberman said, and it’s what his defenders are saying now.