Now that Hillary Clinton has launched her second bid for the White House, we will see even more scrutiny of her on everything from her time at State to the Clinton Foundation’s funders. But the issue that best exposes Clinton’s enormous ambition — and her readiness to sacrifice the interests of consumers to that ambition — is her flip-flop on the corn ethanol tax.

No other active, high-profile American politician has been as duplicitous on a basic pocketbook issue as Clinton has been on this one. The corn ethanol tax, which was imposed by Congress last decade and is formally known as the Renewable Fuel Standard, now costs American motorists $10 billion per year in additional fuel costs. That works out to about $47 per year for every licensed driver in the country.

During her early years in the US Senate, Clinton was a staunch opponent of the corn ethanol tax. In 2002, she and three of her senate colleagues -- New York Democratic Sen. Charles Schumer and California Democrats Sens. Dianne Feinstein and Barbara Boxer — used that very word, “tax” to describe then-pending legislation that was to require the blending of two billion gallons of corn ethanol per year into domestic gasoline supplies. Their March 21, 2002 letter said the pending measure would add “an astonishing new anti-consumer government mandate — that every US refiner must use an ever-increasing volume of ethanol.”

They said consumers would be “forced” to use ethanol and that the legislation was “the equivalent of a new gasoline tax.” In all, during her stint in the Senate, Clinton voted against ethanol 17 times.

But when she set her sites on the White House and realized she had to kowtow – just as Barack Obama was doing – to Big Corn in Iowa, she flipped like a hotcake. In early 2007, during a visit to Des Moines, Clinton said that the US needs to work on “limiting our dependence on foreign oil. And we have a perfect example right here in Iowa about how it can work with all of the ethanol that’s being produced here.”

The sole reason for her flip-flop: her desire to win the Iowa caucuses, which is the first crucially important contest in the race for president. More ethanol production means more money for Iowa farmers and ethanol producers, but it’s a loser for most everyone else in the country. It’s also a negative for the environment and for people who like to eat. John DeCicco, a research professor at the University of Michigan’s Energy Institute, recently published a report which found that “there’s no climate benefit” from using biofuels. Meanwhile, researchers looking at the Gulf of Mexico are expecting another huge “dead zone” (also known as a hypoxia zone) this year, thanks in large part to fertilizer-laden runoff from corn farms in the Midwest.

Furthermore, increased use of ethanol and other biofuels means less land is available to grow food. Last year, the Intergovernmental Panel on Climate Change stated flatly that “there is high confidence that pressure on land use for biofuels will further increase food prices.” [Emphasis in original document.]

But environmental concerns and consumers’ interests are taking a distant back seat to Clinton’s lust for political power. And that desire explains why she’s back in Iowa this week, where she will be campaigning in the town of Monticello, population 3,811. While the residents of Monticello and Jones Country may like the attention they get from Hillary and other prospective presidents, there’s simply no question that by insisting on having its primary first, Iowa has been able to coerce presidential candidates into supporting the corn ethanol tax.

In November 2007, during a speech in Newton, Iowa, she said that if elected president, she would "dramatically increase biofuels production." Clinton's plan was to increase production of fuels like corn ethanol, cellulosic ethanol, and biodiesel to 36 billion gallons by 2022 and 60 billion gallons by 2030.

Thus, in 2002, Clinton opposed the mandated use of just two billion gallons of ethanol per year. But a mere five years later, after seeing that she had to go through Iowa — which produces more ethanol than any other state — to return to 1600 Pennsylvania Avenue, she was advocating the use of 18 times that quantity of biofuel.

As Clinton and her allies said back in 2002, the corn ethanol requirements are an anti-consumer government mandate. Between 2007 and 2014, the cost premium for ethanol over an energy-equivalent amount of gasoline has averaged 92 cents per gallon. Total cost to consumers over that eight-year period: about $83 billion. And the ripoff continues. This year, the RFS will require motorists to purchase about 13 billion gallons of ethanol. (Federal legislators, including, notably, California’s Dianne Feinstein, have filed bills to repeal the RFS.)

To be clear, other presidential hopefuls are also bowing and scraping in front of the corn lobby. Republican Jeb Bush, to his credit, at least says he wants a gradual phase out of the RFS. Rand Paul, that great defender of libertarianism, has proposed legislation that could allow the ethanol scammers to blend even more of their expensive Franken-fuel into our gasoline. Only Texas senator Ted Cruz has come out squarely opposed, calling the RFS “corporate welfare.”

But among the candidates, Clinton stands alone as the one who’s flipped stances on ethanol to one that is diametrically opposed to the interests of consumers. As of Tuesday, there was scant information about Clinton’s energy policies – or any other positions — on her website. Nevertheless, if she were going to buck Iowa’s corn barons she would have said so by now.

Clinton’s ethanol flip-flop is particularly egregious given that she wants to position herself as a champion of the little guy. On Sunday, the Associated Press quoted “senior advisers” from her campaign who said that her focus will be on “strengthening economic security for the middle class and expanding opportunities for working families.”

If she were serious about putting more cash into the pockets of ordinary citizens, she would be opposing the corn ethanol tax. Instead, she supports it. And therein lie two stories: the first illustrates Clinton’s ambition; the second illustrates just how thoroughly Iowa and Big Corn have corrupted the presidential selection process. And that corruption costs American motorists every time they pull up to the pump.