[SampleMan]

Would party leaders pull the plug on his candidacy?

They have no power to do so. Once the delegates vote, they are locked in.

[aruanan]

They have no power to do so. Once the delegates vote, they are locked in.

I don't think so. What the delegates want isn't set in stone. This is why the party came up with the idea of the super-delegates. The party's candidate ultimately is the prerogative of the party. Especially in the Democrat Party, it isn't matter of of one delegate, one vote, the outcome depending on the votes.