By Patrick Appel
James Pethokoukis cites a study by Macroeconomic Advisers:

The Macroeconomic Advisers, LLC (MA) Presidential election model predicts that Democratic presidential candidate Senator Barack Obama will win 54.8 percent of the two-party popular vote and Republican presidential candidate Senator John McCain will receive 45.2 percent in the November election, given economic conditions expected through the fall.... The Presidential election model relies upon four political factorscandidate of the incumbent party, approval rating of the incumbent candidate (if running), party, and incumbent party's term in officeand three economic factorsreal income growth, the unemployment rate, and the change in energy prices. Together, these seven factors predict the share of the two-party popular vote garnered by the incumbent party. This model has correctly predicted the winning party 12 out of 14 times in our sample, and predicted the popular vote better than the original model developed by Ray Fair.... According to this model, an expected 47% increase in the price of oil (WTI) in the three quarters leading up to the election would reduce Senator McCain's vote tally by 2.9 percentage points, while weak real disposable personal income growth over the same period would reduce it by 3.3 percentage points.