Why are we (the United States) subsidizing corn farmers?

From what I understand, corn based ethanol provide very little net energy after taking into consideration the energy used for production. Moreover, using corn for fuel increases food prices. Critics will say Brazil successfully uses sugar cane based ethanol, but sugar cane ethanol is more efficient (produces more net energy) and it is made from waste left over after the extraction of sugar (hence won't affect food prices). Finally, all kinds of ethanol production would ultimately lead to the destruction of rain forest to create ethanol producing cash crops. How is our public policy regarding corn related to the farming lobby? How much are farmers donating to state and federal election campaigns?