Cars run on fuel. Politicians run on votes, and they'll do almost anything to get them. That includes supporting mandates that force us to use ethanol, a fuel made from corn that Iowa farmers grow.

They support ethanol because Iowa is the first state to vote on presidential candidates. Candidates want to look strong at the start of the race, so every four years they become enthusiastic ethanol supporters. Even those who claim they believe in markets pander to Iowa's special interests.

Donald Trump, who doesn't seem to have a consistent political philosophy aside from bashing critics and foreigners, now has joined the ethanol-praising club. In fact, Trump says regulators should force gas stations to increase the amount of ethanol they use. It's a convenient way to attack his Iowa rival, Sen. Ted Cruz, R-Tex., who courageously says the mandate should be phased out.

Cruz is right. Legally mandating that a certain percentage of fuel used be ethanol is a bad idea for several reasons:

First, mandating ethanol means more land must be plowed to grow corn for fuel. The Department of Energy estimates that if corn ethanol replaced gasoline completely, we'd need to turn all cropland to corn—plus 20 percent more land on top of that.

Second, requiring ethanol fuel raises the price of corn—bad news for consumers who must pay more for food.

Third, although ethanol's supporters claim burning corn is "better for the environment," that's not true. Once you add the emissions from growing, shipping and processing the corn, ethanol creates more pollution than oil. Environmental groups such as Friends of the Earth, the Natural Resources Defense Council and the Clean Air Task Force now oppose its use.

Finally, because corn is grown in America, promoters said ethanol would make us more energy independent. Even if the "independence" argument were valid, fracking accomplishes much more. (Anyway, it isn't a valid argument. Trade with Mexico and Canada is just fine. We don't need total independence.)

Since Trump is a businessman, I assume he realizes that ethanol is an expensive boondoggle that wouldn't survive in a competitive market. But in Iowa Trump says, "Ethanol is terrific."

Dr. Ben Carson didn't go that far but according to the Washington Examiner said that it would be wrong to end the subsidies. "People have made plans based on those kind of things," he says. "You can't just pull out the rug out from under people."

It sounds like most politicians want to get rid of subsidies in principle, but never right now—certainly not in the middle of their campaigns. Sen. Marco Rubio says he'd support ending the mandate—after another seven years.

At the Iowa Agriculture Summit, Chris Christie sounded annoyed that President Obama hasn't been more supportive of ethanol subsidies, saying, "Certainly anybody who's a competent president would get that done!"

Bernie Sanders, I-Ver., criticized subsidies in the past, but on Iowa public radio he sounded as if he loves the boondoggle: "We have to be supportive of that effort—and take every step that we could, and in every way we can, including the growth of the biofuels industry."

Of course, big-government Democrats always want to subsidize more. Hillary Clinton says ethanol "holds the promise for not only more fuel for automobiles but for aviation … and for military aircraft; we could be fueling so much air traffic with biofuels. We have just begun to explore what we can do."

Sure. Explore away! That's what market competition does. Entrepreneurs constantly explore options in search of profit. But that's very different from government forcing taxpayers to fund one particular fuel.

Only Cruz and Sen. Rand Paul (R-Ken.) have consistently said that the market, not politicians, should choose fuels. Unfortunately, that principled stance hasn't brought them much support. Presidential-race betting at ElectionBettingOdds.com has Cruz dropping and Paul tied for last.

Energy expert Jerry Taylor is right to say that running for office in Iowa not only means you must praise Christianity; it means being "willing to sacrifice children to the corn god."

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