Stuart Rothenberg agrees:

I’ve become convinced that my initial list of five states probably can be boiled down to just one — one state that is most likely to determine who will be the next occupant of the White House. And that state is Colorado.
If John McCain carries Colorado in November, I’d expect him to hold onto all of George W. Bush’s 2000 states, with the exception of New Hampshire. If he does that, and if Obama holds all of Al Gore’s states, plus New Hampshire, McCain would win 274 electoral votes to 264 for Obama.
If Obama carries the state, he has altered the arithmetic of the Electoral College so as to make it difficult for McCain to win.