The selection of pledged delegates is a somewhat mysterious process, but basically both campaigns have veto power on their own pledged delegates. These two stories highlighted by MSNBC's First Read are one place to start understanding this process.
Will McCaingive up his Senate seat to run for president?
McCain has a very strange aversion to supporting a new G.I. bill.
David Brockwill lead a $40 million effort to attack McCain.
The University of California may sic a collection agency on Hillary Clinton.