Congress did not mandate all automobile fule to be mixed with ethanol.
What's mandated is all the metro area that're currently using MTBE as
oxygenate to reduce air pollution shall switch to ethanol as an
oxygenate.

For the areas that're NOT currently required to have oxygenated
gasoline, there's no federal requirement to add ethanol into the fuel.
Certain states may have separate ethanol requirements.

Honestly, the ethanol industry in this country doesn't even have the
produciton capacity to supply a nation wide ethanol mix of 2%. They
can barely supply the current requirement the replace MTBE in those
metro areas and the ethanol price is shooting through the roof.