When Mitt Romney was asked at a New Hampshire town hall in June 2011 about climate change, he probably did not think he was taking a risk by admitting that it is happening. “I believe based on what I read that the world is getting warmer,” said Romney. “Number two, I believe that humans contribute to that…. And so I think it’s important for us to reduce our emissions of pollutants and greenhouse gases that may well be significant contributors to the climate change.”

The science on the subject is clear, and Romney had said the same in the 2008 without inviting a notable backlash. But this time was different. Rush Limbaugh, the godfather of modern conservative talk radio, reacted with horror. Romney had just demonstrated himself too credulous of science and Enlightenment reasoning to win the Republican nomination. “Bye-bye nomination,” Limbaugh intoned. “Another one down. We’re in the midst here of discovering that this is all a hoax. The last year has established that the whole premise of man-made global warming is a hoax, and we still have presidential candidates who want to buy into it!”

Limbaugh’s assertion that Romney could not win the Republican nomination was premature; Romney remains very much in contention. But right-wing voters have held Romney’s statement against him as they continue to search for a suitable alternative.

The brouhaha might seem strange to an outsider, since Romney did not actually propose to do anything about climate change. In his campaign book No Apologies, Romney dismissed cap and trade as “radical feel-good politics.” But the conservative media no longer accept objective facts—the facts themselves must now fit the right-wing narrative. Joseph Lawler, then the managing editor of The American Spectator, explained the closed-circuit epistemology as a means of guaranteeing a preferred policy outcome: “Expressing skepticism of the science behind climate change, as for instance Gov. Rick Perry has, allows candidates to assure voters that they won’t support cap and trade or carbon taxes once they’re in office.”

Sure enough, the next time Romney discussed climate change publicly, at a town hall in Dover, New Hampshire, in August, he softened his earlier comments, saying, “I think the Earth is getting warmer…. I think humans contribute to that. I don’t know by how much. It could be a little. It could be a lot.” By late October, Romney had turned into a full-fledged climate change denier. “My view is that we don’t know what’s causing climate change on this planet,” he said at a fundraiser in Pittsburgh.

This episode—the bullying of an educated executive vying to be leader of the free world into the denial of demonstrable facts—was a striking demonstration of the sway Limbaugh and his cronies in conservative media hold over Republican hopefuls. It’s a degree of influence unmatched by any entity on the left, or for that matter by issue activists on the right. (The anti-tax Club for Growth also put out a white paper attacking Romney’s climate change apostasy, but it garnered far less attention than Limbaugh did.) And as the Republican primary unfolds, the consequences of the right-wing media megaphone are clear: the ideological discipline meted out by the pundits is a big part of the reason Republican candidates are sticking so relentlessly to doctrinaire conservative positions during this campaign cycle, and why there is often so little space between them.

Limbaugh, who invented the modern right-wing talk radio format and spawned a generation of imitators, is not the only pundit who thinks he is more powerful than actual elected officials: in October, Sean Hannity invited Rep. Ron Paul (R-TX) on his radio program and spent most of the interview lecturing Paul for having had the audacity to criticize him. But Limbaugh is the only one for whom it is undeniably true. “The candidates who run afoul of Limbaugh are marked for death,” says Thomas Fiedler, dean of the College of Communication at Boston University. “Talk radio, and Limbaugh in particular, has defined what the acceptable limits are for the candidates,” Fiedler adds. “They’ve clustered themselves much farther on the right end of the spectrum.”

For the conservative media, the task of whipping Republicans into line isn’t limited to the official campaign. During the debate over health care reform, former public supporters of the individual mandate—including presidential candidates-to-be such as Newt Gingrich and Romney—abandoned their prior positions and lined up against “Obamacare.” Amid the hyperventilating about “death panels,” as the party’s prospective standard-bearers fell into line, it became politically untenable for GOP legislators to negotiate even on a bill whose roots lay in conservative proposals. The Affordable Care Act ended up passing nonetheless—and Republicans in Congress had no influence over the law.

Ben Adler covers climate-change policy for Grist and is a contributing editor for CJR