Edwards’s decision to champion the cause of activists is not one scientists typically make; they avoid political controversies for a reason. In 2011 the American Association for the Advancement of Science, the largest scientific society in the world, commissioned a paper on the “standards, benefits and risks” of advocacy. “When scientists become advocates, they become ‘partisans’ and are no longer neutral conveyors of scientific information,” the paper stated. “While the line between neutral and partisan, between dispassionate and passionate, is not easily drawn, it nonetheless exists.” Scientists who transgress that line tend to have their credibility impugned. Just ask the climatologists. Or think of Rachel Carson, who was a scientist with the United States Fish and Wildlife Service before she became an author. Upon the publication of “Silent Spring” in 1962, critics accused her of hysteria and Communism.

Consider the case of Clair Cameron Patterson, the geochemist who first determined the age of the planet from lead isotopic data. While working with that data, Patterson discovered, in the early 1960s, that scientists had grossly underestimated the amount of lead we were adding to the environment. There was lead in our gasoline, in our paint, in canned tuna, in our plumbing. The lead levels in the bodies of postwar Americans were 700 to 1,200 times as high as those of their preindustrial ancestors, Patterson estimated. For more than 20 years, the lead industry resisted his campaign to ban the metal from consumer products. The United States didn’t remove the last of the lead from gasoline until 1996. Though our lead levels are still around 10 to 100 times as high as those of our preindustrial ancestors, they have, on average, been coming down ever since. But in 1965, when Patterson first began sounding the alarm about lead, prominent toxicologists dismissed him as a “zealot” who had abandoned science for “rabble rousing.”

Edwards considers Patterson a role model. He would prefer to remain dispassionate, he says, but his experiences in D.C. and Flint taught him that neutrality carries its own risks. If, as surveys suggest, Americans are less willing to defer to the authority of scientific experts than they once were, scientists themselves are partly to blame, Edwards believes. In the academy, competition over a dwindling pool of funding and the pressure to publish have created “perverse incentives,” he said in a recent interview with The Chronicle of Higher Education. As a result, “the idea of science as a public good is being lost,” and along with it, the “symbiotic relationship” between the scientific community and the public. For him, his intervention in Flint was a kind of demonstration project, a case study of how to conduct science ethically, in the public sphere and for the public good.

Michigan officials initially tried to discredit him, too, trotting out the rabble-­rousing charge. Although the state “appreciates academic participation in this discussion,” Wurfel, the Michigan Department of Environmental Quality spokesman, wrote in an email to a local reporter last September, “offering broad, dire public-­health advice based on some quick testing could be seen as fanning political flames irresponsibly.”

A scientist abiding the paper commissioned by the American Association for the Advancement of Science would have responded to Wurfel dispassionately, perhaps by conveying his data in a peer-reviewed journal. Instead, Edwards fought back like some 21st-­century pamphleteer. On a website one of his graduate students built, flint​water​study​.org, he ­posted, along with incriminating documents and helpful tips for Flint residents, acerbic commentaries condemning Wurfel and other officials he considered culpable. “You wish they’d listen to reason, scientific facts, the truth,” he told me. “But if they’re corrupt, the only weapon you’ve got is ridicule.”

In Flint, Edwards’s pugilistic brand of advocacy seemed to work. Last winter, Wurfel and other officials resigned. In February, Congress invited Edwards to testify at hearings devoted to the Flint crisis, and in a rare display of bipartisanship, Democrats and Republicans alike solicited his opinions not only on matters of science but also on matters of policy and morality and the law, treating him as a sort of oracle or ombudsman. It was hard to recall a scientist who had received a warmer reception on Capitol Hill. Gov. Rick Snyder had by then acceded to the demand spray-­painted on the Block, appointing Edwards to the task force overseeing the state’s response to the emergency in Flint. The E.P.A. awarded Virginia Tech an $80,000 grant to retest the city’s water. Edwards had done as much as anyone to expose the betrayal of public trust in Flint. Who better than him to restore it?