The distance between New York and Washington, D.C., is 313 miles, a number that became especially relevant last week to activist Adam Eidinger as he prepared to set out on foot for the capital, along with hundreds of other food activists, farmers, and business leaders.

“Many organic leaders realized this past spring that, basically, we don’t have a friend in the White House,” says Eidinger, who hopes the march will accomplish what good will could not. “We’re going over the cliff here. This is very much a personal thing with the president now.”

Candidate Barack Obama made many promises, but one in particular—“We’ll let folks know if their food has been genetically modified, because Americans should know what they’re buying”—has become an ever more potent rallying cry for supporters of organic foods. The march comes just as the Food and Drug Administration considers a legal petition to require the labeling of genetically modified foods, known as “Frankenfoods” by critics. Such foods are already prolific in our diets; the Grocery Manufacturers Association estimates that 80 percent of processed foods now contain ingredients that have been genetically modified.

“We have a campaign promise, an unprecedented coalition, and an election year,” says the Center for Food Safety’s Andrew Kimbrell, who is leading the FDA drive with the support of groups like Consumers Union, which publishes Consumer Reports. Add in recent deadly outbreaks of salmonella and listeria, and the coalition also sees an unusually ripe moment to change the nation's food policy.

What caused the simmering rage at Obama to boil over? A small flowering plant in the pea family, Fabaceae, known as alfalfa.

It started last fall when a small group of CEOs from companies like Whole Foods and Stonyfield sat down for a private chat with Agriculture Secretary Tom Vilsack. They had come to personally plead their case: genetically engineered crops and their capacity to drift into and taint organic crops were no longer a small-scale problem.

One fact was indisputable: genetically engineered crops are having a heyday. Since 1996, the U.S. acreage in GMO (for "genetically modified organism") soybeans has grown from 7 to 94 percent, with GMO corn skyrocketing from 1 to 88 percent of cultivation. Now the USDA was considering a petition for approval of “Roundup Ready” alfalfa, engineered by Monsanto to be herbicide- and pesticide-tolerant. Alfalfa holds a special status in the organic community. As a key feed for cows, it’s inextricably linked to milk, often considered the gateway product for families new to organic foods.

“We were not there to cry out our baby-blue eyes over ethics,” says Stonyfield’s Gary Hirshberg. After all, the $29 billion-a-year organic industry is now one of the fastest-growing sectors of U.S. agriculture and a rising source of jobs; its failure could have a real impact on food, farmers, and rural communities as well as consumers nationwide. “We were there to talk about money.”

Inside the Beltway, a new term in the national agricultural debate was catching on: “coexistence.” Vilsack, a former Iowa governor and farmer advocate, was its champion, trying to find common ground between what have become the two fastest-growing—and incompatible—trends in food. “It’s emotional for the organic guys, it’s emotional for the agriculture-production guys, and it’s emotional for me,” Vilsack confided to The Daily Beast. “They should work together instead of trying to beat each other up. It’s nuts.”

But the chance of yet another GMO crop drifting into and tainting the heart of their industry was too much for the organics leaders. “This is a pivotal issue for the 21st century,” says Hirshberg, who has to buy soy for his yogurts from Canada, now that 92 percent of soy in the U.S. is genetically modified. “It’s about an explosion of toxic chemicals accompanied by the deregulation of these crops, and there are many more crops in the pipeline.”

Just before last Christmas, Vilsack broke with tradition and called the squabbling organic, conventional, and GMO players to a windowless, bunkerlike Ag Department room with the goal of quickly finding common ground on alfalfa. There was some grumbling and eye-rolling from all sides at the last-minute nature of the summons. Still, farmers from around the country called in on conference lines, and working groups were formed. But within days Vilsack was being publicly vilified, including in the Wall Street Journal op-ed pages, for creating a precedent to “permanently politicize a system that is supposed to be based on science.” The secretary fought back, arguing that “the rapid adoption of GE [genetically engineered] alfalfa has clashed with the rapid expansion of consumer demand for organic foods” and that “surely” some better solution would be found.

But it wasn’t. Vilsack denies reports of administration or lobbying pressure, but in late January the administration greenlighted the unregulated planting of bioengineered alfalfa, along with two other bioengineered crops—sugar beets and a type of corn used in ethanol production. In July the Department of Agriculture announced it wouldn’t regulate a Roundup Ready strain of Kentucky bluegrass. The organics crowd cried foul, and even Vilsack will admit he’s hamstrung: the regulations at his disposal hark back to 1950, long before anyone envisioned a genetically modified sugar beet.

A study released last month by the D.C.-based watchdog group Food & Water Watch reports that between 1999 and 2009, some $547 million was spent on lobbying and campaign contributions to ease regulatory oversight and prevent labeling of genetically engineered crops. It also outlines the potential risks of biotech foods, such as increased allergies, the rise of so-called superweeds, and unknown long-term health effects in humans. A Canadian study this year found that the blood of 93 percent of pregnant women sampled and 80 percent of their umbilical-cord blood contained a pesticide put into GMO corn by Monsanto. “We’ll see in 20 years, after the guinea pigs"—consumers—"have all used these products,” says George Siemon, CEO of Organic Valley, the nation's largest organic-farming cooperative. “I’m really disillusioned.”

The biotech boosters beg to differ. Genetically engineered crops are researched and designed with a slew of benefits in mind: drought resistance, reducing the need for pesticides, increasing production and driving down costs, reducing soil erosion, and helping to feed the world. Tom Helscher of Monsanto says that while some GMO ingredients do end up in food products like oil, “it’s not genetically modified oil—it’s just oil.” And Mark McCaslin of Forage Genetics, which helped create the alfalfa seed with Monsanto, says there is “zero” effect of his alfalfa on a cow’s milk and that demand for his new seed is already robust. “About 10 to 20 percent of the seed planted this year will be Roundup Ready—probably about 5 million acres. If we look out five years ahead, it’s reasonable to expect that one third to one half of all alfalfa fields could be Roundup Ready.”

Still, "Big Ag" producers are feeling nervous. In California, there is talk of exploring a 2012 ballot initiative to require the labeling of GMO foods. Bob Stallman, president of the American Farm Bureau Federation, has just launched the U.S. Farmers and Ranchers Alliance with an $11 million annual budget (including funds from genetic-seed giant Monsanto and chemical-pesticide creator DuPont), to address consumers on everything “from labels to animal welfare to biotech,” he says. “And to assure them it’s not an ‘us vs. them’ thing.”

As the fight for mind share continues, Eidinger and his fellow marchers head for the capital, hoping to get consumers on their side. But the biggest question of the moment is politics. A slew of agricultural subsidies is set to expire next year, and the first genetically modified animal—a salmon—is currently under review by the FDA for human consumption.

Is there an Obama doctrine on food, and if so, what is it? Is the president opening the regulatory floodgates, as critics claim, to an accelerated new Frankenworld of food? Or is he a beleaguered champion, like his wife, of organic eating and just can’t beat back the “Big Ag” lobby?

The Obama administration, says food author Michael Pollan, is "playing a complex game, trying to appeal to both camps.” And, for now at least, leaving consumers guessing.