In his roundup of November’s first batch of polls, Nate Silver notes they have tightened but that McCain is still far outside the 3-point margin he needs to change the race. Should he close that window, the election will come down to five states: Virginia, Colorado, Pennsylvania, Ohio, and Nevada. (Such a narrowing would likely hand McCain states like North Carolina and Florida.) If we grant that Obama will win Colorado, where he leads big in early voting, Obama will need to win Pennsylvania, Ohio, or Virginia and Nevada to surpass 270 electoral votes. Included in Silver’s calculations is the precious insight that, at this point, Obama is more likely to win Arizona than McCain is Pennsylvania.