When it comes to the US election, national polls can be very misleading. This is because of how the contest is Balkanized into states and electoral college votes. It doesn’t matter if you barely manage to win a state, or if you win by a huge majority. As explained on this post on The Economist’s Democracy in America blog, the winner will be whoever gets more than 270 electoral college votes:
Barack Obama already has 260 votes either “strong” or “leaning”. John McCain has just 112 strong and 64 leaning. He must not lose a single “lean” state to keep himself 86 votes behind.
Now those swing states… Mr McCain has tiny leads in Nevada and North Dakota, and slightly bigger ones in North Carolina and Florida. Mr Obama has clear leads in Colorado, Virginia, Ohio, New Hampshire, Alaska (you can probably write that one off now, though) and Montana.
This may be a partial explanation for the surprise selection of Sarah Palin as John McCain’s running mate. While national polls show McCain and Obama neck-in-neck, the electoral college projections look much worse for the Republicans. That may have encouraged them to employ a riskier strategy, in hopes of changing the dynamics of the race.