Gasoline prices always are a key factor in politics each summer, starting from Memorial Day in May, through the busy summer driving and vacation season, to Labor Day in early September. This will be especially so this year as Congress debates biofuels policy and other energy issues. These include the Keystone XL pipeline, the Environmental Protection Agency's (EPA) proposed rule on reducing sulfur emissions, and the federal budget, which has many petroleum industry tax provisions on the table. Thus, it is worth a look at what the Department of Energy is predicting for summer gasoline prices.According to the Energy Information Administration (EIA), both gasoline and diesel prices are down. The average retail price of regular gasoline acros...