In the nation’s agricultural heartland, farming is more than a multibillion-dollar industry that feeds the world. It could be on track to become a right, written into law alongside the freedom of speech and religion. Some powerful agriculture interests want to declare farming a right at the state level as part of a wider campaign to fortify the ag industry against crusades by animal-welfare activists and opponents of genetically modified crops. The emerging battle could have lasting repercussions for the nation’s food supply and for the millions of people worldwide who depend on U.S. agricultural exports. It’s also possible that...