Congress has not mandated. It would be absolute lunacy if they did. You should try working the math of how much ethanol that is and what it would take to produce it. We certainly don't have the process plants to create that much nor the available land to grow the crops needed.
Here is a previous FreeRepublic discussion to start the math.
The fuel rule change was to restrict the use of MTBE. Ethanol is just one way to meet the reformulated and oxygenated gasoline requirements.
Do you know the difference between fact and hypothesis? You don't refute one with the other.