That rule of politics collapsed resoundingly in the 2012 campaign when five of the six top Republican candidates said it was time for such intervention in the private market to end.
Now, Iowa's senior political leaders are pondering how to shore up political support for the corn-based fuel at a time when its economic and environmental benefits are under attack.
The latest blow came this month, when the Obama administration proposed cutting the required amount of ethanol in the nation's fuel supply for the first time since Congress established a standard in 2007.
The state's leading Republicans and Democrats hope they can still use Iowa's political importance as a swing-voting state and as the site of the first presidential nominating contest to get candidates to support keeping the requirement, or at least part of it, in place.
But the case has become a tough sell for Republicans as the party has moved to the right and become increasingly hostile to government programs and directives.
Even among Democrats, concern has grown about ethanol's role in rising food prices and in cultivation of land that had been used for conservation.
