Despite lower crude prices, ethanol plants across the nation continue to operate at a brisk pace. Photo: Associated Press For decades, presidential candidates have bowed to Iowa’s corn-based ethanol industry while campaigning in a state where corn is king. But several of the likely Republican candidates slated to address the state’s agricultural industry on Saturday backed the sunset of ethanol subsidies in 2011, and many oppose the industry’s new sacred cow: the renewable-fuel standard, which requires blending ethanol and other biofuels into the gasoline supply. How the likely White House contenders navigate the issue will signal how much Republican politics are now driven by the party’s conservative base, which balks at government interference in the marketplace. Two GOP contenders who want to phase out the renewable-fuel standard, Florida Sen. Marco Rubio and Louisiana […]