Turns out he botched more than just that joke, or at least, that’s the excuse he’s using. The fact that he’s a charisma black hole with a tin political ear who didn’t stand a remote chance against Hillary, Obama, and Edwards might have also factored into it.

The big question now: which of them will he taint with an endorsement?

Kerry, a Massachusetts Democrat, plans to say he will remain in the Senate to recommit himself to efforts to extricate the United States from the war in Iraq. His decision to stay out of the presidential race reflects a realization that he would have had an uphill climb in capturing the Democratic nomination, given the other party heavyweights who are already in the race, according to the officials, who spoke to the Globe on condition of anonymity…

Kerry, the party’s 2004 presidential nominee, has been acting like a 2008 candidate virtually since he lost to President Bush — traveling the country, spreading money to other Democratic candidates, and keeping in place a campaign infrastructure that was ready for another presidential bid.

But according to Kerry associates, the senator’s plans changed dramatically in the fallout of his election-eve “botched joke” about the education levels of US troops. The harsh reaction to that incident — from many Democrats as well as Republicans — displayed to Kerry the extreme skepticism within his own party about whether he should mount another run.

Update: Here’s Kerry’s statement. He went out doing what he does best: encouraging withdrawal and defeat.

Update: Tinti’s got the video of him choking up on the Senate floor. It’s at the very end.