The federal ethanol subsidy is pure pork if you live outside the dozen states that produce the corn-based gasoline alternative and a major support to agriculture and cleaner air if you live within them. But whatever its value as a fuel, ethanol is proving once again to be more accurate than any poll at picking presidential nominees.

The subsidy for ethanol, at $600 million annually, is but a small piece of the nation’s transportation funding, which comes in at well over $200 billion a year. It is also an annoying piece, because the congressional delegation from Ethanol Country – Kansas, Iowa, South Dakota, Minnesota, etc. – no sooner are confronted with evidence that the product is not needed then they devise another excuse to keep the subsidy pipeline pumping. If ethanol doesn’t produce less pollution than gasoline, then it protects against the oil crisis. If there is no oil crisis, then it helps farmers. If mostly large corporations benefit, then it creates jobs. And so on.

The federal government publishes study after study showing that ethanol is an expensive failure, yet the subsidy lives on. It survives, in part, because it performs a service for which people who live outside the ethanol region have yet to say thanks. Every four years, packs of presidential aspirants stand in tears amid the Iowa corn because somewhere in their careers they said something unkind about the subsidy. It’s akin to telling the good voters of New Hampshire that you’ve never really liked maple syrup.

Iowans are swift about their rejection. Their primary is early and the test is simple. In ’96, Sen. Phil Gramm, who in his career defended the interests of oil produced in his state of Texas, didn’t stand a chance in Iowa against the champion ethanol defender, Sen. Bob Dole of Kansas. Now it is Sen. John McCain’s turn to be rejected. Sen. McCain is not so much concerned about oil as he is about wasteful spending, and when that topic comes up, ethanol inevitably does too.

The Wall Street Journal last week quoted an Iowa Republican observing that Sen. McCain’s fight against pork means he couldn’t get elected dog catcher around here. A loss in Iowa doesn’t end a presidential run, but it sure slows it down, meaning that Iowans perform the service of using the narrowest, most parochial of measures to clear out the field of candidates, limiting the choices for all other voters.

Maine might be outraged by this behavior if it weren’t for the news from North Dakota, which is planning to build a new ethanol plant in Grand Forks using the peelings of potato-processing factories to make the fuel. Potatoes, hmmm … those arguments from Ethanol Country may have merit after all.