The Iowa caucuses were only the first in a long train of presidential primaries and caucuses to come. But Monday’s results shot down once and for all the myth that no candidate can win Iowa without kowtowing to the ethanol lobby.

For years, would-be presidents stumping in Iowa treated the federal subsidy for corn-based ethanol subsidies as a sacred cow that had to be worshiped even if it meant abandoning the free-market principles they purported to embrace. Mitt Romney, campaigning in Iowa in 2011, posed for photographers while holding an ear of corn. “I support the subsidy of ethanol,’’ he declared. John McCain, who had once ripped ethanol subsidies as corporate welfare for agribusiness, took to telling audiences all over the state that he had seen the light and now drank a glass of ethanol every morning for breakfast.

But after a strong win this week by Senator Ted Cruz of Texas, the ethanol lobby’s power to intimidate presidential candidates is over.

Cruz was unabashed in his rejection of the federal ethanol mandate, known as the Renewable Fuel Standard (RFS). Though he represents a major oil-producing state, he has opposed subsidies for all energy sources, arguing that a level playing field and a free market would be better for consumers, producers, and the economy.

That stand led Iowa’s ethanol industry to mount a fierce statewide campaign against him. Iowa’s Republican governor, Terry Branstad, abandoned his longstanding policy of not making pre-caucus endorsements, and urged voters to defeat Cruz because he is the “biggest opponent of renewable fuels.’’ (Branstad’s son, perhaps not coincidentally, is the state director of a pro-ethanol organization.)

As the nation’s largest producer of corn, ethanol, and biodiesel, Iowa’s attachment to the RFS can’t be overestimated. Polls have consistently showed that a large majority of Iowans support the ethanol mandate, and candidates like Donald Trump were glad to use the issue against Cruz.

“He will destroy your ethanol business 100 percent,’’ Trump insisted in his final pitch to Iowa voters on Monday. “Your ethanol business, if Ted Cruz gets in, will be wiped out within six months to a year. It’s gonna be gone.’’

In the end, however, Iowa Republicans didn’t hold Cruz’s principled position on ethanol against him. Not only did he win Monday’s GOP caucuses, he drew more votes than any previous Republican presidential candidate. Cruz even came in first in several of Iowa’s top corn-growing counties — including Kossuth County, which produces more corn than any other in the Hawkeye State.

It has long been clear that the case for ethanol preferences is dubious. The federal mandate distorts US agriculture, drives up the price of food, and reduces fuel efficiency. Researchers now know that it also increases atmospheric carbon dioxide, since the ethanol production cycle releases considerable amounts of CO2. In the past, fear of an Iowa backlash deterred presidential candidates from discussing the Renewable Fuel Standard candidly. Happily, those fears have now been laid to rest. No more is ethanol a political third rail, not even in Iowa.