The 2016 hopefuls are already trekking to Iowa — just as the Environmental Protection Agency is considering a reduction in the required percentage of ethanol in gasoline. The two events are anything but unrelated.

The ethanol requirement, conceived to encourage renewable energy, has been sustained despite its counterproductive effects by the lobbying of a rising ethanol-agribusiness complex and the politics of those first-in-the-nation presidential caucuses, held among the sprawling cornfields of the Hawkeye State. From 1988 to 2004, I was part of that process as an adviser to Democratic presidential candidates. I thought it was a no-brainer to stump for ethanol and a no-go zone to oppose it.

At the start, the campaign promises reflected not only strategic calculation, but arguably the best of intentions. By now, it's painfully and patently clear — and it has been for a while — that the ethanol mandate may be good politics, but it's a putrid policy that pollutes the environment, propels global warming instead of slowing it, inflates food costs and imperils food supplies.

Today, 44 percent of all corn grown in America feeds the ethanol machine, not consumers at home or hungry people abroad. The relentless drive to convert food into fuel has plowed up 5 million acres of conservation land and virgin prairie, "releas[ing] massive amounts of carbon dioxide that has been locked in the soil." Those who profit from ethanol claim it's a clean fuel. The University of Nebraska geologist Darryl Pederson points out that this is a case of convenient math: It doesn't count "emissions" during fermentation or consider ethanol's production, which heavily relies on fossil fuels, fertilizers, planting, harvesting and transport. He concludes that we'd be better off, in terms of energy let alone the environment, "if a given field were covered with solar cells."

The evidence is cumulative and compelling. According to Science magazine, the greenhouse gases pouring out of plowed up conservation land mean that it would take nearly half a century before new ethanol plants could even start reducing carbon dioxide. Instead, the ethanol industry is pushing up corn prices and squeezing food stocks at home and abroad.

Let me reiterate that candidates didn't know all this when they took up the ethanol banner, at least in earlier years. Still, they were always apparent of the political imperative. Former Vice President Al Gore has been remarkably candid here. As he said in reversing his own position on ethanol two years ago, "I had a certain fondness for farmers in the state of Iowa because I was about to run for president." Frankly, we didn't think twice about this in the Gore campaign — or four years later, when another leading environmentalist, John KerryJohn Forbes KerryFeehery: Oprah Dem presidential bid unlikely Dem hopefuls flock to Iowa Change in Iran will only come from its people — not the United States MORE, was running. They both won Iowa and the nomination. And Howard Dean, the self-proclaimed truth-teller, didn't win either despite his full-throated pander on ethanol: Let our farmers, not "Saudi sheiks," profit from energy production.

Barack ObamaBarack Hussein ObamaMcCarthy: ‘No deadline on DACA’ Democrats will need to explain if they shut government down over illegal immigration Trump’s first year in office was the year of the woman MORE and Hillary ClintonHillary Diane Rodham ClintonIntel Dem decries White House 'gag order' after Bannon testimony 'Total free-for-all' as Bannon clashes with Intel members Mellman: On Political Authenticity (Part 2) MORE were there in 2008 — in Iowa and for ethanol. They happily toured ethanol plants; so did Mitt Romney and Rudolph Giuliani. This was such a rite of passage in Iowa that John McCain, an early critic of the "boondoggle," morphed into a "strong" advocate of ethanol because of greenhouse gas-reducing effects. A political science professor at the Iowa State University explained: "You can't trash ethanol and expect to win in Iowa." McCain didn't win; but he clipped enough votes from Romney to hand victory to Mike Huckabee, the man he could and did beat.

It was a little different in 2012. Rick Santorum, who favored phasing out ethanol subsidies, edged out Romney — sort of — in a late count and by 34 votes. The Iowa Republican electorate is increasingly and adamantly conservative, anti-subsidy and anti-government. 2016 hopefuls like GOP Senator Rand PaulRandal (Rand) Howard PaulNSA spying program overcomes key Senate hurdle Fix what we’ve got and make Medicare right this year Despite amnesty, DACA bill favors American wage-earners MORE can cater to that; Paul voted against $5 billion for ethanol earlier this year. But what about Chris Christie, who would almost certainly have to carry the general electorate in Iowa in a close contest? Or Hillary Clinton, Joe BidenJoseph (Joe) Robinette BidenDemocrats will need to explain if they shut government down over illegal immigration Trump thinks he could easily beat Sanders in 2020 match-up: report Biden marks MLK Day: Americans are 'living through a battle for the soul of this nation' MORE, or former Maryland Governor Martin O'Malley, a long shot who needs an early upset in the state's caucuses?

I respect and appreciate the Iowa caucuses. For Democrats, they've been level-headed predictors of the eventual nominee. They're also a political safety net for ethanol.

There's one person who can transcend this and still sit in the Oval Office. He's already there. Obama is never running again — in Iowa or anywhere. He can lead the way not just to reduce the ethanol mandate, but to eliminate it. He can act in the spirit of John Kennedy, who was asked at a press conference if he would second his predecessor's call for term limits for members of Congress. To laughter, Kennedy replied: That's "the sort of proposal which I may advance in a post-presidential period, but not now." Obama isn't post-presidential, but he is post-electoral; and by now he surely understands the false promise and the real dangers of corn-based ethanol.

President Kennedy believed that American agriculture could serve larger purposes. He created a landmark program called Food for Peace. Today, impelled by politics and the precedence of the Iowa caucuses, we're making life harder for the kind of people abroad that Food for Peace was designed to help, and for millions of hard-pressed families here struggling to pay their grocery bills. In the name of the environment, we're poisoning the atmosphere and amplifying the tides of climate change. And it's time, well past time, to stop.

Shrum, a senior fellow at NYU's Wagner School of Public Service, was a senior advisor to Dick Gephardt in 1988, Al GoreAlbert (Al) Arnold GoreDems face hard choice for State of the Union response Washington governor proposes new carbon tax The Renewable Fuel Standard is broken beyond repair MORE in 2000 and John Kerry in 2004.