Why do people say Dean is finished if he doesn't endorse kerry?

[ProudToBeLiberal]

People are saying that he will be finished from the democratic party. If Dean doesn't get the nomination I think he will campaign against Bush but, he won't outright support kerry. I think Dean trancends party lines so if the Democratic party turns their back on him I think he can hold his own. He has enough supporters to help him without the democratic party. It's not going to be Dean who looses out but the Democratic party if they turn their back on Dean.