OK, I'm going to be the bad guy and ask...
How realistic is it for Bill Clinton to withdraw from the primary due to his wife being in a car accident (and likely passing away), then turn around a week later and start campaigning for Gore? An endorsement? Sure. But to start traveling the nation right after a car accident that forced you from the race seems a bit much.
Granted, Tsongas jumping on the campaign trail right after withdrawing for no apparent reason seems a bit sketchy, but at least I'm trying to slowly step into it.