There's one issue that can turn an election - the economy.

Charlie Cook says there's rarely an issue more important for an incumbent than the economy.

Barack Obama has fair to middling approval ratings, but he has negative ratings from voters when it comes to the economy.

Obama badly needs the country’s economic performance over the next six months to validate his policies and decisions. If the overall economy improves, job creation increases, and consumer confidence goes up, those markers will serve as validation. If the economy is bouncing along, with growth at a subdued level and unemployment still at or above 8 percent—not the 9 percent of a year ago, but hardly in the 7.2-to-7.4 percent range that boosted President Reagan’s 1984 reelection fortunes after the 1982 recession—the public will be in no mood to validate Obama’s policies and decisions.

Gallup’s most recent polling suggests that Obama has received a bit of a boost from the decline in gasoline prices; his approval rating bumped up to 50 percent in three consecutive days of Gallup’s three-day moving averages. The bump shows just how volatile public attitudes are, particularly when important economic issues are involved. That volatility isn’t likely to change between now and Election Day. The economy will determine this election.