"I don't like McCain, but at least he is adhering to the notion of the party pulling together after the primaries. Something a few freepers would be well-served to emulate."
I think he knows that he is going to need every conservative vote he can get and at this point in time he doesn't have enough. So he needs to "up his credibility" in order to make a run for POTUS in '08. Frankly anyone that is considered hawkish on illegal immigration is probably not voting for him and is also now wondering what is wrong with their guy Graf, that an OBL such as McCain would support him.
I sincerely doubt that McCain's endorsement will erode Graf's conservative support. McCain is doing what Kolbe should have done when Graf won the primary - back the GOP nominee.
I very much doubt anyone on the pro-enforcement side is overly worried that a Minutemen got McCain's endorsement. Graf has solid credentials.
McCain also endorsed Blackwell in Ohio, Santorum in Penn, Kyl in Arizona...he's a political animal trying to make political connections in preparation for his '08 run so they'll rally their constituencies to vote for him in the primaries and, in his dreams, general.
It's that simple.