Dropping the initial H (which makes "an historic" correct) has been going on for a long time in American English. I don't see anything wrong with it, as long as the speaker is consistent.

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Actually, a little research indicates that "historic" (and related words) actually used to be pronounced with a silent h, and it's only a relatively modern event that the h is pronounced. So using "an historic" is somewhat archaic, but still not technically incorrect.

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I just listened to the McCain sound-bite, and have to say that it never occurred to me that someone might say "an historic" without dropping the h. That is definitely incorrect.

It depends on if the 'h' is pronounced. I don't think I've ever said it, but if I slip into the accent of one of the other languages I speak (Spanish, perhaps), the 'h' can easily go, and then my grammar Nazi takes over and changes 'a' to 'an.' Easy.

Actually, I think using "an" with h words is the old fashioned and the British way...I could be wrong though.