There are, by now, more than a few theories about the rise of Donald Trump, and how views long considered too extreme for national politics earned him the Republican nomination for president. But perhaps no concept appears to explain this process as neatly as the Overton Window. Best known until recently as the title of an overheated political thriller by Glenn Beck, in the last year the Overton Window has been cited everywhere from The New York Times to The Rachel Maddow Show. Despite its peculiar origins and limited applications, pundits increasingly invoke it to describe not only Trumpism, but the Sanders surge, Brexit, and more.

The Overton Window refers to the range of policies on any given issue that are, at that moment, popular enough for a politician to campaign on successfully. Just outside of the window lie “acceptable” policies, and beyond those the “radical” and “unthinkable.” Joseph Overton, a libertarian think tanker who developed the concept at the Mackinac Center for Public Policy in Michigan in the mid-1990s, sought to move this “window of political possibilities” and bring unpopular ideas into the mainstream. The most effective way to do this, he proposed, was not to advocate for minor, incremental changes to an already accepted idea, but to make the case for a currently “unthinkable” idea, stating it cogently and provoking an informed discussion. These efforts would make radical ideas look more normal, nudging them into the “acceptable” category, and eventually making them politically viable.

Trump’s candidacy, many liberal commentators have suggested, exemplifies Overton’s strategy. By floating extreme policies (build a wall on the Mexican border, ban Muslims from the United States), he has seemingly forced public debate sharply to the right. Meanwhile, the resurgence of socialist politics embodied by Bernie Sanders and British politician Jeremy Corbyn, as well as the passage of right-to-work laws in several states, increasing restrictions on abortion, and the UK’s referendum on EU membership are said to fit the same pattern. Rachel Maddow devoted a segment to the Overton Window before her interview with Sanders last December, explaining how he could shift the consensus leftward. After the jolt of Brexit, John Lanchester began his 5,000-word lament in the London Review of Books with a primer on the concept.

It’s easy to see why the Overton Window holds such appeal. For one thing, it offers a universal theory of change in an age of polarization and fracture. While Trump and the UK Independence Party pull right, and Sanders and Corbyn pull left, Overton’s concept suggests that the mechanism of change is the same. For another thing, it has the virtue of simplicity: Overton did little more than repackage the basic negotiating principle that if you ask for a lot, you will likely get more than if you ask for a little. And although the window offers a theory of change, its central element—the window itself—actually describes the norm from which reality has deviated. Zeynep Tufekci worries in The New York Times that Trump “voices truths outside the Overton Window,” while the British writer Sam Leith speculates that Corbyn may have positioned his party “dangerously far from the centre of the Overton Window.” The window serves as shorthand for the erstwhile consensus. Viewing politics through the Overton Window reinforces liberal notions about the moderate center, even as that center ground erodes.

For conservatives, by contrast, the Overton Window has always been about strategy. Though Overton himself never committed his most influential idea to paper, his Mackinac Center colleague Joe Lehman continued his work after Overton’s death in 2003 at age 43. Lehman not only coined the term “Overton Window,” he weaponized it, setting up training sessions on the concept for other right-leaning think tankers. The term filtered into the conservative blogosphere in 2006, when Josh Trevino enthused about the window as a tool for the right. “Step by step, ideas that were once radical or unthinkable—homeschooling, tuition tax credits, and vouchers—have moved into normal public discourse,” Trevino declared. “The conscious decision to shift the Overton Window is yielding its results.”

The concept did not reach a wider audience, however, until Glenn Beck cast Overton’s ideas as the bogeyman in his 2010 best-seller, The Overton Window. The villain of Beck’s tale is Arthur Gardner, an aging PR guru who plots to use the Overton Window to foist his own objectives (“criminalize dissent,” “reinforce dependence and collectivism”) on an unsuspecting and gullible public. In his afterword, Beck urges readers to watch out for manipulation in their own lives and to set their own priorities.

While Beck shared Overton’s libertarian ideology, he was wary of the window as a strategy for change, imagining a totalitarian left that could hijack it. Its elitist overtones also stuck in his craw: An early champion of the Tea Party, Beck preferred to extol the power of the American people, whereas Overton largely sought to influence policy-making from the top down by “educating lawmakers and the public.” At one point in his novel, Beck takes a veiled swipe at the somewhat otherworldly Mackinac Center, which was founded on an island in Lake Huron: Arthur Gardner’s son boasts that his father “stole the concept” of the Overton Window “from a think tank in the Midwest.”

Beck’s novel met with disapproval from libertarian policy wonks. “Joe Overton deserved better,” one critic mourned in Liberty magazine. But it helped to create the popular impression of the Overton Window not as a strategy to advance principled political beliefs, but as a conspiratorial plot. “We put a false extreme at both ends,” one of the characters reveals, “to make the choices in the middle look moderate by comparison.” Thanks to the novel’s success—it debuted at the top of The New York Times best-seller list and sold 329,000 copies in its first six months—this view has stuck. Where we once talked about shifts in public opinion, we now talk about the Overton Window moving, implying an unfair tampering with the consensus.

This is perhaps the Overton Window’s biggest drawback as a theory of change: It tells us more about the handful of activists who supposedly move the window than the voters whose opinions actually change. While Trump has certainly lowered the standard of debate on the right, he didn’t have to move the consensus rightward; he played to a bloc of voters who already found his proposals desirable. Sanders, too, connected with bottom-up movements such as the Fight for $15 and Occupy Wall Street. To chalk up their successes to shock tactics is to ignore the long-simmering populism that swept both right and left in the presidential primaries. It is impossible to understand what drives these movements without engaging with the economic and cultural circumstances that underpin them.

The more divided we become, the harder it is to locate the Overton Window, let alone move it. There is now a window of policies that are acceptable to the Republican base, and another for Democrats, but on the national level, there is no window. Instead of a consensus edging one way or another, we have a choice between two poles. The Overton Window is ultimately a name for what we have lost, not an indication of where we are headed. Its popularity today represents a powerful nostalgia for the center. It doesn’t help us overcome fragmentation or rebuild a consensus. Its attractiveness lies in its reassurance that a middle ground once existed.