That sentence is mind-boggling bad! I tend to make mistakes of this kind, with my highly qualified draw-out compound sentences (like this one ;-)), so I pay attention to fix them. But this? WOW. It took me a good while to parse it at all.

I would prefer a slightly reordered version of gustavolacerda's sentence:

"Pennsylvania, previously considered Democratic, is seen by McCain's supporters as a potential swing state, with just six days to go."

Or put the final clause up front, to get it "out of the way", of the main content of the sentence. Any comments on what would be preferable?