I think even die-hard Dean fans (I've been a moderate one since CMB dropped) accept that Dean's door has closed. But his biggest role in this election has yet to be played out.
Dean gets 18% in Wisconsin tonight. I think many would agree that those who still vote for Dean are his hardcore supporters, the ones unlikely to leave until he quits. What would happen if he dropped and threw his support behind Edwards?
Even if only 2/3 of Dean supporters switched to Edwards at his urging (far more than would likely switch to Kerry at this point) it could put Edwards in front. Dean's backers bring votes and volunteers, but more importantly money, which Edwards really needs.
Gephardt suicide-bombed Dean in Iowa. Might Dean return the favor with Kerry? Edwards will need a Northerner with executive experience to put in the number two slot, and if Dean could deliver him a huge boost towards the nomination...
Regardless, more than anything, what Dean does next could severely impact the race, or what's left of it.