Well, if we use this metric and the USA Today forecast, Obama will be facing lower economic growth than what Bush faced in '92 and his son faced in '04. That's real nail-biter territory. The regression line suggests Obama getting 50.9 percent of the vote, although, as the graph shows, that line is being pulled upward a bit by Eisenhower's unexpectedly good performance in 1956. If you take out that case, the Obama forecast is 50.03 percent of the vote. In other words, don't expect to get a lot of sleep on election night next year.
All the usual caveats apply here. The forecast for 2012 economic growth is just a prediction -- it could get substantially better or worse. And this is just a bivariate regression model, which doesn't include things like foreign policy or ideological extremism or campaign quality. And, of course, past performance does not necessarily predict the future.
But this could be a really, really close race.