These are precisely the issues that have given rise to the so-called food movement. Yet that movement has so far had more success in building an alternative food chain than it has in winning substantive changes from Big Food or Washington. In the last couple of decades, a new economy of farmers’ markets, community-supported agriculture (also known as farm shares) and sustainable farming has changed the way millions of Americans eat and think about food. From this perspective, the food movement is an economic and a social movement, and as such has made important gains. People by the millions have begun, as the slogan goes, to vote with their forks in favor of more sustainably and humanely produced food, and against agribusiness. But does that kind of vote constitute a genuine politics? Yes and no.

It’s easy to dismiss voting with your fork as merely a lifestyle choice, and an elite one at that. Yet there is a hopeful kind of soft politics at work here, as an afternoon at any of America’s 7,800-plus farmers’ markets will attest. Money-for-food is not the only transaction going on at the farmers’ markets; indeed, it may be the least of it. Neighbors are talking to neighbors. Consumers meet producers. (Confirming the obvious, one social scientist found that people have 10 times as many conversations at the farmers’ market as they do at the supermarket.) City meets country. Kids discover what food is. Activists circulate petitions. The farmers’ market has become the country’s liveliest new public square, an outlet for our communitarian impulses and a means of escaping, or at least complicating, the narrow role that capitalism usually assigns to us as “consumers.” At the farmers’ market, we are consumers, yes, but at the same time also citizens, neighbors, parents and cooks. In voting with our food dollars, we enlarge our sense of our “interests” from the usual concern with a good value to, well, a concern with values.

This is no small thing; it has revitalized local farming and urban communities and at the same time raised the bar on the food industry, which now must pay attention (or at least lip service) to things like sustainable farming and the humane treatment of animals. Yet this sort of soft politics, useful as it may be in building new markets and even new forms of civil society, has its limits. Not everyone can afford to participate in the new food economy. If the food movement doesn’t move to democratize the benefits of good food, it will be — and will deserve to be — branded as elitist.

That’s why, sooner or later, the food movement will have to engage in the hard politics of Washington — of voting with votes, not just forks. This is an arena in which it has thus far been much less successful. It has won little more than crumbs in the most recent battle over the farm bill (which every five years sets federal policy for agriculture and nutrition programs), a few improvements in school lunch and food safety and the symbol of an organic garden at the White House. The modesty of these achievements shouldn’t surprise us: the food movement is young and does not yet have its Sierra Club or National Rifle Association, large membership organizations with the clout to reward and punish legislators. Thus while Big Food may live in fear of its restive consumers, its grip on Washington has not been challenged.

Yet. Next month in California, a few million people will vote with their votes on a food issue. Already, Prop 37 has ignited precisely the kind of debate — about the risks and benefits of genetically modified food; about transparency and the consumer’s right to know — that Monsanto and its allies have managed to stifle in Washington for nearly two decades. If Prop 37 passes, and the polls suggest its chances are good, then that debate will most likely go national and a new political dynamic will be set in motion.

It’s hard to predict exactly how things will play out if Prop 37 is approved. Expect the industry to first try to stomp out the political brush fire by taking the new California law to court on the grounds that a state cannot pre-empt a federal regulation. One problem with that argument is that, thanks to the bio-tech industry’s own lobbying prowess, there is no federal regulation on labeling, only an informal ruling, and therefore nothing to pre-empt. (I believe this is what is meant by being hoist with your own petard.) To avoid having to slap the dread letters on their products, many food companies will presumably reformulate their products with non-G.M. ingredients, creating a new market for farmers and for companies selling non-G.M. seed. The solidarity of Monsanto and companies like Coca-Cola — which reaps no benefit from using G.M. corn in its corn syrup — might then quickly crumble. Rather than deal with different labeling laws in different states, food makers would probably prefer to negotiate a single national label on G.M. foods. Consumer groups like the Just Label It campaign, which has collected 1.2 million signatures on a petition to force the F.D.A. to label G.M. foods, thus far to no avail, would suddenly find themselves with a seat at the table and a strong political hand.

One person in Washington who would surely take note of the California vote is President Obama. During the 2008 campaign, he voiced support for many of the goals of the food movement, including the labeling of G.M. food. (“We’ll let folks know whether their food has been genetically modified,” he declared in an Iowa speech in 2007, “because Americans should know what they’re buying.”) As president he has failed to keep that promise, but he has taken some positive steps: his U.S.D.A. has done much to nurture the local-food economy, for example. Perhaps most important, Michelle Obama began a national conversation about food and health — soft politics, yes, but these often help prepare the soil for the other kind. Yet on the hard issues, the ones that challenge agribusiness-as-usual, President Obama has so far declined to spend his political capital and on more than one occasion has taken Monsanto’s side. He has treated the food movement as a sentiment rather than a power, and who can blame him?

Until now. Over the last four years I’ve had occasion to speak to several people who have personally lobbied the president on various food issues, including G.M. labeling, and from what I can gather, Obama’s attitude toward the food movement has always been: What movement? I don’t see it. Show me. On Nov. 6, the voters of California will have the opportunity to do just that.