While the way he was treated is disgusting, an "ABC Radio" ID card is not a "press credential", and Graham is wrong to represent it as such, both at the event and in this blog entry.
ABC, like all the other MSMs, has specific ID cards for members of its news division. If you work for ABC in a news capacity, you carry two IDs, one that specifically says "ABCNEWS" on it, and another one that just says "ABC", which is nothing more than your company ID card that lets you past the guard in your own building every day. (Oh, and also grants you a very substantial discount at the Disney Store down at the mall.)
What Graham was carrying was the latter, and it gives him no more privileges to gain access to any event than the company ID card of someone who works at Burger King. In fact, he technically committed a fireable offense by using it as such, though given that his job is to make waves (and thus get ratings), I'm sure his bosses won't care. They sure would if anyone else at WMAL got caught trying something like this, though.
Where are our nasty attorneys. Sue the bastards!!! Call the FBI this is a civil rights violation.