“Dark Money” relates the personal story of the Koch family in considerable detail — an engineer father who made a fortune building oil refineries, then spent the last years of his life as an angry member of the John Birch Society; an early conversion by Charles and David Koch to the radical libertarian economics of Friedrich Hayek and Ludwig von Mises; a web of sibling rivalry among all four of the family’s brothers, ending in painful legal confrontations that dragged on for years.

Mayer also sheds some useful light on the co-conspirators who helped the Kochs build a movement that spread far beyond electoral politics. Richard Mellon Scaife, heir to the Mellon banking fortune and to much of the wealth of Gulf Oil, was the financial presence behind the Heritage Foundation. John M. Olin, whose family chemical corporation was a major beneficiary of federal weapons procurement, focused on the creation of faculty positions for conservatives at prestigious university campuses. The Bradley brothers, Harry and Lynde, used proceeds from the merger of their family electronics firm with Rockwell International to underwrite a whole array of publishing and research ventures.

But the main goal was to win elections, and in that crusade the Kochs and their allies had the benefit of federal laws that they played no part in promulgating. One was the section of the Internal Revenue Code that allows for 501(c)(4) organizations, ostensibly devoted to “social welfare” but permitted to engage in electoral politics in an essentially unregulated way. A 501(c)(4) is not required to disclose the sources of its funding, and that provision alone has brought in huge amounts of money from donors eager to contribute but reluctant to identify themselves. The 501(c)(4) loophole has been around since the early 20th century, but it was given new vigor in 2010 by the Supreme Court’s Citizens United decision, which removed virtually all limits on corporate campaign funding and fostered its anonymity.

What were all these organizations and donors promoting, other than the election of Republican candidates to office? Free-market orthodoxy, to start with. “Market principles have changed my life,” Charles Koch declared in the 1990s, “and guide everything I do.” That seems as true in 2016 as it was when he said it. Closely related to free-market faith is the hatred of regulation, federal, state or local. “We should not cave in the moment a regulator sets foot on our doorstep,” Charles once wrote. “Do not cooperate voluntarily; instead, resist wherever and to whatever extent you legally can.”

This ideology helps to explain one of the most important Koch crusades of recent years: the fight to prevent action against climate change. The Koch-sponsored advocacy group Americans for Prosperity has been at the forefront of climate-change opposition over the past decade. When the Republicans took over the House of Representatives in 2011, Americans for Prosperity lobbied lawmakers to support a “no climate tax” pledge, and by the time Congress convened that year, 156 House and Senate members had signed on.

As ferocious as they have been in defense of free-market ideas, the Koch brothers are also acting out of tangible self-interest, Mayer argues. The Kochs made their money in the carbon business; they have diversified far beyond it over the years, but a stiff tax on carbon could have a significant impact on their bottom line. Mayer reports that an E.P.A. database identified Koch Industries in 2012 as the single biggest producer of toxic waste in the United States. The company has been in and out of federal court over the years as defendants in cases alleging careless and sometimes lethal flouting of clean-air and clear-water requirements. Several have paid tens of millions in fines to settle these cases. It is plausible that the Kochs and some members of their network are participating in politics largely to keep their fortunes intact. “They said they were driven by principle,” Mayer writes of the Koch-led network, “but their positions dovetailed seamlessly with their personal financial interests.”