Obama opens a lead with seven weeks to go

As little as two weeks ago, polling put the ball game between Barack Obama and Mitt Romney as a tie. From Sept. 3 to Sept. 6, the RealClearPolitics average of polls put the race at an exact statistical dead heat.

Today, in the aftermath of the Democratic National Convention, the same average of polls has Barack Obama up 48.6 to 45.5 over Mitt Romney, a 3.1 point lead. 3.1 points sounds small, but in the realm of national politics, where elections are frequently won by a point or less, 3.1 is a considerable advantage. Even after factoring in a typical post-convention “bounce” for Obama and the general inaccuracy of polling far from election day, Nate Silver at The New York Times calculates this polling advantage translates into a 72.6 percent chance of an Obama victory in November. Online prediction markets largely concur, with Intrade quoting Obama at a 65.5 percent chance of victory and Betfair giving him a 72.5 percent likelihood of winning.

If Obama maintains these numbers for one or two more weeks, he will be on course to win the presidency by close to 100 electoral votes, taking all of the states he took in 2008 with the exception of Indiana and North Carolina. And even if his numbers fall (as they might in the comedown from a convention bounce), Obama will remain a slight favorite in two states that Romney must win, Ohio and Florida, as well as a slight favorite in three states that Romney must win at least two out of three of: Colorado, Iowa, and Virginia.

These national numbers don’t give Mitt Romney much room to breathe. While he could conceivably open up a new battleground in Nevada, Wisconsin, or New Hampshire, Obama has similar opportunities in Montana, Missouri, Indiana, and North Carolina. In all likelihood, the dynamics of the race are already decided: Romney and Obama will spend most of their time fighting over Ohio, Florida, Virginia, Colorado, and Iowa, and Romney will need to chalk up considerably more victories against worse odds in order to take the presidency.

Compounding Romney’s troublesome need to win four out of five of these states is that the five lack any strong commonality that would lend itself to a campaign theme designed to scoop them all up. The impact of the recession varies considerably across these five states, with unemployment in Florida a full 3.5 points higher than it is in Iowa. Attitude toward Washington varies considerably too, with voters in Virginia much more sympathetic to “Washington insiders” than the nation at large. Demographic differences exist as well, with large Hispanic populations in both Florida and Colorado, but a largely white electorate in the other three. And finally, the five states differ in terms of their dominant economic activities. This diversity makes it very hard to craft a message that will connect with all five of the states; winning two or three, by contrast, is a much simpler affair.

Plenty can change in seven weeks, and challengers to the presidency have come back from graver deficits than this. But at the moment, with Mitt Romney behind and no obvious way to put himself ahead, smart money must be on Democrats to hold onto the White House.