Under federal law since 2007, gasoline in America has been blended with more and more corn-based ethanol every year. President Obama has been a major supporter but today, for the first time, his Environmental Protection Agency will reduce the mandate. A political explosion is already underway in Washington, pitting corn producers against an unlikely alliance, including oil companies and environmentalists. Is ethanol failing to help clean up the air after all? Is excessive corn production threatening the environment? What's likely for the price of gasoline?