Remember when climate change could be a bipartisan issue? Newt Gingrich and Nancy Pelosi did an advertisement together, boasting of their partnership on the challenge it posed. John McCain also believed that man-made climate change was an urgent problem. Now it’s virtually impossible to find any leading Republicans, including potential Presidential candidates, who will agree, without equivocation, on all of these points: that temperatures are rising, that human beings caused it, and that the nation and the world must take action to address it.

Republicans are unified in denial, and one good reason this is so is the Supreme Court’s decision in the Citizens United case. That decision revolutionized the law of campaign finance; what is less well recognized is that it transformed the climate-change debate, too. Justice Anthony Kennedy’s majority opinion in Citizens United, in 2010—the Justices were divided 5–4—began the Super PAC era in American politics. At the time, the decision was most remarked upon for its assertion that corporations possessed a right to freedom of speech, under the First Amendment, much as individuals do. In fact, this part of the case was neither new nor particularly controversial. (Courts have granted corporations, like newspapers, First Amendment records for decades.) Far more important was the assertion in Citizens United that money is speech—that money contributed in support of a political campaign is entitled to full First Amendment protections. This result led, in turn, to the conclusion that individuals could give unlimited amounts to support any candidate they wanted, as long as the money was controlled by a nominally independent entity, not the campaign itself. These independent entities are now known as Super PACs, and they spent more than half a billion dollars in the last election. The gist of the Citizens United decision is that the Supreme Court gave rich people more or less free rein to spend as much money as they want in support of their favored candidates. Sometimes, as with Super PACs, the money supports candidates directly. Other times, the money goes to 501(c)(4) organizations, groups with occasionally shadowy aspects to them that are supposed to refrain from direct advocacy for candidates but in fact clearly push voters in one direction or the other.

Citizens United had the effect of taking money and power away from the political parties—which control only modest amounts of money, by contemporary standards—and handing that power to the people who write the checks. Certain of these people, the newly empowered rich, care a great deal about climate change—about denying its existence and fighting attempts to limit its impact. No one is quite sure who gives how much to the 501(c)(4)s, because they are allowed to keep their donors’ names secret. But it’s clear that in the forefront of anti-climate-change activism are the Koch brothers, who have invested huge amounts in politics and political candidates since Citizens United. (Jane Mayer has written about the brothers’ efforts.) The Kochs are so prominent that they have become, in effect, gatekeepers for Republican politics. Climate-change denial is now the price of admission to the charmed circle of Republican donors. Indeed, Americans for Prosperity, an organization heavily supported by the Kochs, has created a pledge for officeholders to sign, which promises that they will not support any legislation related to climate change that increases government net revenue. Dozens have signed on, including such likely Presidential candidates as the senators Ted Cruz, Rand Paul, and Marco Rubio.

It is true that Democrats and the scientific community are not entirely powerless in this debate. One well-known billionaire, Tom Steyer, has announced plans to spend as much as a hundred million dollars to support candidates who will address climate change. But no one should be mislead that this has somehow been a fair fight. According to the Center for Responsive Politics, conservative groups spent roughly two hundred and sixty-five million dollars in the 2012 election cycle, and liberal groups spent about thirty-five million. To those in the carbon-producing business (like Koch Industries and the oil companies), the regulation of global warming is seen as an existential threat; they will spend what they can to stop it. For everyone else—that is, those merely affected by climate change—the threat is (at least for now) largely diffuse or abstract. For most people, it’s hardly even a voting issue, much less one that prompts them to write checks. The check writers are the denialists, and the Supreme Court gave them an immensely powerful hand.

David Koch arrives at a benefit at the Metropolitan Museum of Art. Photograph by Carlo Allegri/Reuters.