On Tuesday, Thom Tillis, the speaker of the North Carolina House of Representatives, held off a libertarian challenger backed by Rand Paul to win the Republican nomination for U.S. Senate. Tillis was widely considered the establishment candidate, though not because his politics were notably more moderate than his Tea Party rivals’. As House speaker, Tillis proudly blocked the expansion of Medicaid in North Carolina, and he oversaw a decidedly radical legislative agenda that included restrictions on abortion and voting rights.

What marked Tillis as the candidate of the establishment was the source of his financial support, which included “nearly $2.5 million in television ads and mailers paid for by groups such as American Crossroads, the U.S. Chamber of Commerce and the National Rifle Association,” the Washington Post reported. Americans for Prosperity, bankrolled by Charles and David Koch, has already sunk millions of dollars into North Carolina in the past twelve months, to soften up Tillis’s opponent, the vulnerable Democratic freshman Kay Hagan. The Democrats, for their part, have also turned to outside billionaires and “dark money” groups to defend Hagan and their thin Senate majority. Even before Tuesday’s primary, national interest in the North Carolina Senate race had made it the third costliest contest in the country.

In recent years, North Carolina has become a showcase for the unfettered flow of money into American politics. The retail magnate and mega-donor James Arthur Pope, whom Jane Mayer wrote about in the magazine three years ago, has wielded enormous influence in the state. Wealthy liberal donors have tried to catch up, but they have a long way to go. In 2010, thanks in part to the support of Pope and allies like the Kochs and Karl Rove’s American Crossroads PAC, Republicans took control of both houses in the state legislature for the first time since 1870. In 2012, Pat McCrory became the state’s first Republican governor in nearly two decades; last year, he named Pope the state’s budget director.

After a series of Supreme Court rulings, from Citizens United, in 2010, to McCutcheon, last month, the outsized influence of big donors now enjoys robust legal protection—as long as there is no “effort to control the exercise of an officeholder’s official duties” or “quid pro quo corruption,” in the words of Chief Justice John Roberts. In North Carolina, the debate over whether unrestricted campaign spending represents the flourishing of democracy or its corrosion is not an abstract one. It is literally in the water. For many years, environmental and community activists alleged that state officials had an inappropriately close relationship with Duke Energy, the nation’s largest electric utility, which is headquartered in Charlotte. Those allegations grew louder when McCrory, who worked at Duke Energy for twenty-nine years, arrived at the governor’s mansion.

On February 2nd, an employee at a disused Duke coal plant in Eden noticed that a coal-ash pond had breached through a storm pipe into the adjacent Dan River. No one knows how long the spill had been going on, but by the time it was under control an estimated thirty-five million gallons of slurry had entered the river. The ash coated the bottom of the waterway and raced downstream toward drinking-water intakes from Danville, Virginia, to the Atlantic Ocean.

Coal ash—the stuff left over after coal is burned to generate electricity—contains significant amounts of arsenic, lead, selenium, mercury, and other heavy metals. It can cause skin irritation and respiratory problems, and is toxic if ingested; some of its chemicals can contribute to cancer. It is also damaging to fish, wildlife, and vegetation. Some of the waste, known as “fly ash,” spews out of coal-plant chimneys into the surrounding air. “Bottom ash” is left behind in the furnaces, and often gets transferred to holding pits nearby. The Eden plant closed in 2012, to make way for another Duke Energy operation that ran on hydraulically fractured natural gas. The company apparently did not have plans to move the sixty-three years of ash that had built up in the old plant.

Suddenly, people across North Carolina began wondering if coal-ash ponds next to the plants in their neighborhoods were safe. Investigators quickly found that they were not. Probable violations of clean-water statutes were found at Duke Energy sites across the state, many in plants situated near poor or majority-black communities.

After the Dan River spill, more questions arose about Governor McCrory’s relationship with his longtime employer. Later in February, the U.S. Attorney’s Office for the Eastern District of North Carolina opened an investigation to look for evidence of outright corruption, which forced some embarrassing disclosures: Duke Energy worked with environmental regulators to keep information about potential dam breaches secret from the public, and caused deliberate failures on the part of the state’s Department of Environmental and Natural Resources (D.E.N.R.) to force Duke to clean up unlined coal ponds.

For fourteen of the twenty-nine years that he worked for Duke Energy, mainly in the human-resources and economic-development departments, McCrory simultaneously served as mayor of Charlotte, the state’s largest city. He resigned from the company when he ran for governor, but remained a shareholder. Duke Energy and its employees and subsidiaries spent three hundred thousand dollars on his bids for the governorship, according to the National Institute on Money in State Politics. (Serving as a mayor and holding a job in the private sector is “common throughout the state,” Joshua Ellis, a spokesman for McCrory, told me. “All North Carolina mayors are part-time.” He added, “This notion that Duke has been getting any favorable treatment is totally untrue.”)

The company does not seem to have suffered during McCrory’s time in office, however. One of his first moves as governor was to remake D.E.N.R., by installing John Skvarla III, a businessman who had been the C.E.O. of a company whose portfolio included cleaning up fracking sites, at the helm. D.E.N.R.’s budget was cut and federal offsetting grants were refused. Agency staff complained about a severe weakening in enforcement abilities; some were laid off and others resigned. Within months, Skvarla could brag about having turned “North Carolina’s No. 1 obstacle of resistance into a customer-friendly juggernaut.”

Before the spill in February, environmental groups had tried to bring a suit against Duke over improper coal-ash storage under the Clean Water Act, only to have D.E.N.R. intervene. The agency negotiated a settlement with Duke worth only ninety-nine thousand dollars, with no requirement for a cleanup. “Here, the normal relationship between the law enforcement and the law-abiding citizens was stood on its head,” Frank Holleman, a senior attorney for the Southern Environmental Law Center, which has been trying to sue Duke Energy over previous violations, said. “The law enforcer and the law breaker have been acting hand in glove.”

Duke—founded by the same family as the nearby university, but otherwise unrelated—makes no bones about its political involvement. Its activities range from donating millions to campaigns through its political-action committee, DUKEPAC, to encouraging employees to run for office, “generally, school boards and town councils,” a Duke spokesman, Tom Williams, said. “You know, the old mantra of a utility: citizenship and service.”