By Evan Halper, Tribune Washington Bureau (TNS)

The fortunes of the wonder fuel that promised to help clean the environment, secure America and save small family farms have steadily dwindled as environmentalists, food advocates and auto enthusiasts sour on its promise. Now that fuel, corn-based ethanol, finds itself threatened with a defection that was once unthinkable: Iowa voters.

The electorate here in the early voting state often defined by its vast expanses of corn has long demanded that candidates pledge allegiance to government production mandates for millions of gallons of ethanol, the homegrown product. But as the 2016 White House hopefuls traverse the state, they are seeing that Iowans have grown strikingly ambivalent.

The Republican presidential contender now polling strongest in Iowa, Ted Cruz, is campaigning on an energy platform that would have been a death wish in elections past. Cruz, the U.S. senator from Texas, is an unabashed opponent of giving ethanol any special government help. He derides it as the worst kind of central planning. He champions legislation to wipe out the decade-old Renewable Fuel Standard, which mandates large amounts of ethanol get blended into the nation’s gas supply.

“Voters here are just not that interested in ethanol anymore,” said Steffen Schmidt, a professor of political science at Iowa State University. “You don’t even hear the word come out the mouths of candidates much.”

There are myriad reasons, not the least of which is a modern-day Republican electorate that takes pride in bucking the established order and is increasingly absolute in its disdain for subsidies. But it is also about the shifting politics of renewable fuels in a state where small family farms have given way to much bigger agribusinesses. Only a fraction of the state’s voters work in the corn industry these days. There is as much buzz on the campaign trail in Iowa about wind power as there is about ethanol.

It is all compounded by troubles befalling the decade-old ethanol mandate, signed into law by George W. Bush, that transcend Iowa but now appear to be giving voters pause even there. Cars are more efficient and people are driving fewer miles than the drafters of the law had anticipated, leaving auto manufacturers to warn that engines are at risk of malfunction if the federal government doesn’t ease quotas of ethanol blended into retail gasoline.

Environmentalists once hopeful the product would help curb global warming now caution that it may be just as harmful to the planet as fossil fuels.

And even as Iowa’s longtime GOP governor, Terry Branstad, warns that candidates who tangle with ethanol could find their presidential aspirations buried by Iowans, a much more influential force in Midwestern politics is sending the opposite signal.

Koch Industries, the behemoth energy firm run by billionaire political donors Charles and David Koch that itself has a major interest in ethanol, despises the mandate. In an April letter to Congress, the company called it “an unqualified failure that should be repealed in full,” reflecting growing disdain among Republican activists for any programs that prop up renewable fuel industries.

Cruz drew from that zeitgeist at an Iowa agriculture summit earlier in the year at which several of the GOP candidates appeared. “I recognize that this is a gathering of a lot of folks who the answer you’d like me to give is ‘I’m for the RFS, darn it.’ That’d be the easy thing to do,” he said at the event. “But I’ll tell you, people are pretty fed up, I think, with politicians that run around and tell one group one thing, tell another group another thing, and then they go to Washington and they don’t do anything that they said they would do.”

But ethanol industry leaders in the state say Cruz will pay a heavy price. They have been running radio advertisements for the last couple of weeks that accuse the Texan of hypocrisy, pointing to tax breaks and other government support enjoyed by the oil industry that Cruz favors. Among those targeting Cruz is Branstad’s son, Eric, who formed a pro-ethanol group called America’s Renewable Future.

“Senator Cruz and anyone else who wants to say this is not an issue in Iowa is mistaken,” Eric Branstad said. “Iowa voters are only now starting to pay attention to the campaign. And they are beginning to learn where Senator Cruz is on this.” Branstad says his group has persuaded some 50,000 Iowans to pledge to caucus only for candidates who support the fuel standard.

Branstad predicts Cruz’s star will fall as a result of his anti-ethanol crusading. Donald Trump sought this month to regain ground he lost to Cruz by highlighting the Texan’s obstinance on energy policy.

But while nobody argues that Cruz can’t get knocked out of the pole position, many doubt ethanol would be the reason.

“It’s helped him polish his credentials as a tough guy,” said Dennis Goldsford, a professor of political science at Drake University in Des Moines. “Republican voters here are more concerned about ISIS and Obamacare than this.”

Despite a recent industry poll concluding that large majorities of likely caucus goers, “once informed about the Renewable Fuel Standard and biofuels,” would be more likely to vote for candidates who support them, the issue barely registers on independent voter surveys. When Iowans are asked what their biggest concerns are this election season, ethanol — and agriculture issues in general — don’t even rank.

©2015 Tribune Co. Distributed by Tribune Content Agency, LLC.

Photo: Republican U.S. presidential candidate Senator Ted Cruz speaks during the Republican presidential debate in Las Vegas, Nevada December 15, 2015.    REUTERS/Mike Blake