OF ALL the theories to explain the unexpected success of Donald Trump’s presidential campaign, this, surely, is the most novel. Forget about a disaffected working class buffeted by globalisation and automation, pent-up racial resentments finding an outlet or the advent of the 24-hour news cycle. No: in the assessment of Daniel Drezner, a professor of international politics at Tufts University, it’s the political scientists who are to blame.

Although clearly tongue-in-cheek, this hypothesis sounds less absurd now than it would have done before 2008, the year that four American academics brought out a book called “The Party Decides: Presidential Nominations Before and After Reform” (TPD). The book’s main thesis is that political parties have formidable power to influence voters in presidential primaries.

TPD was never a bestseller. Nonetheless, it has gained more attention from journalists than any political-science book in recent memory. According to Google News, 763 articles have cited TPD’s title since the start of 2011. Just over 500 more contain its catchphrase “invisible primary”, which describes how candidates compete for support from party grandees before the first votes are cast. Such coverage is comparable only to that received by bestsellers like “Dreams From My Father” by Barack Obama (758) or Michael Lewis’s “Moneyball” (784).

During Mr Obama’s presidency, a new generation of young journalists has emerged who are focused on Washington, DC. They eschew the sources, leaks and scoops that are pursued by their more traditionally minded colleagues in favour of the sage counsel of academic political science. Many of these whizz-kids have treated TPD with awed reverence. For much of 2015 they dismissed Mr Trump’s chances in the Republican primaries by relying on the book’s claim that parties usually guide voters towards “acceptable” nominees. But it was precisely by making such overconfident pronouncements, Mr Drezner argued recently in the Washington Post, that the authors sowed the seeds of their own demise.

Scientists are well acquainted with the “observer effect”, which, in physics, for example, stipulates that the characteristics of a subatomic particle can never be fully known because they are changed by the act of measuring them. Similarly, wrote Mr Drezner, “The Party Decides” has been “the primary theory driving how political analysts have thought about presidential campaigns. It seemed to explain nomination fights of the recent past quite well.” However, in previous elections, there were no crowds of journalists citing TPD. This time, says Mr Drezner, Republican decision-makers “read smart take after smart take telling them that Trump didn’t have a chance…so GOP party leaders didn’t take any action. Except that the reason smart analysts believed Trump had no chance was because they thought GOP leaders would eventually take action.”

The 2016 primaries are putting political science—as exemplified by TPD—to a very public test. Republicans in Congress have already sought to cut off public funding for research in the discipline. Now, if it is seen to have failed, it will slow down the steady advance into the mainstream media that the field has made over the past eight years—and could possibly bring it to a halt.

When journalists write about gravitational waves, they talk to scientists. When they write about interest rates, they talk to economists. But until recently, when they wrote about elections, they often pretended that academic expertise did not exist. “In 2005, when I came to Washington,” writes Ezra Klein, a founder of Vox, an “explanatory-journalism” site, “knowing political science wasn’t a legitimate form of knowing about politics, or at least it wasn’t presented as one to young journalists like me.” The numbers bear him out: since 2006 there have been 7.5 references to “economist” in the New York Times for every mention of a “political scientist”.

A political (journalism) revolution

Theories abound to explain this imbalance. One hypothesis is self-segregation: journalists with a penchant for numbers are likely to gravitate towards covering obviously quantitative fields, whereas those with a more narrative bent may prefer politics. Another is the availability of sources. There is no one person who can speak for, say, consumers or debtors as a whole, so economic journalists must resort to experts who study aggregate behaviour. In contrast, politics is conducted by a small number of individuals who are usually keen to talk to reporters, making outsiders’ analysis seem redundant. Arthur Lupia of the University of Michigan argues that, whereas fields like economics can seem “objective” and technical, political issues are visceral, emotional and tribal. People hold immovable beliefs about politics, he concludes, and have no inclination to defer to “impartial experts” on such topics. And Mr Drezner thinks that there is little appetite among either reporters or readers for the dispiriting structural analyses that are professors’ stock in trade.

Throughout George W. Bush’s presidency, most American political reporters were allergic to any numbers more advanced than a cherry-picked poll result. The tide did not start to shift until 2008, when Nate Silver, a baseball writer who developed statistical expertise by predicting how players would perform, began posting forecasts for that year’s topsy-turvy primary elections online as an anonymous blogger. Mr Silver used techniques that any political scientist would find familiar.

Thanks to rigorous analysis and a sterling track record—he was bullish on Mr Obama’s chances long before the Iowa caucuses, and correctly called 49 of 50 states in the general election—Mr Silver developed a devoted following. Eager to test the audience for what would soon be called “data journalism”, in 2010 the New York Times began hosting his blog, which he called “FiveThirtyEight” for the number of votes in America’s electoral college. Even Mr Silver, who by that point was a well-known forecasting whizz, could not have predicted how big the market for his cleverer-than-thou takes would become: on the eve of the 2012 election 20% of the visitors to the paper’s website read “FiveThirtyEight”.

Mr Silver’s success set off a modest paradigm shift in political journalism. Perhaps his biggest draw was his thinly veiled disdain for the innumerate punditry that ruled the airwaves. Mr Silver delighted in savaging commentators who relied on vapid clichés like “momentum shifts” and “game-changers”. And unlike any other commentator in Washington, he was willing to put his money where his mouth was.

In October 2012 Joe Scarborough, a television presenter and former congressman, took aim at Mr Silver, writing: “Anybody that thinks that this race is anything but a toss-up right now is such an ideologue, they should be kept away from typewriters, computers, laptops and microphones for the next ten days, because they’re jokes.” Mr Silver promptly tweeted him an offer of a $2,000 bet that Mr Obama would win, which Mr Scarborough wisely passed up. Mr Silver had brought the rules of political science to Beltway journalism: no longer were all opinions equally valid. Some interpretations were right, some were wrong, and every election provided a new opportunity to put them to the test.

Like all good businesses, “FiveThirtyEight”—which was acquired by ESPN in 2013—quickly attracted imitators and competitors. Mr Klein started Vox, the New York Times established a new quantitatively minded section, called “The Upshot”, and the Washington Post annexed a blog, called “The Monkey Cage”, dedicated to political science. What was once Mr Silver’s lonely crusade soon became an echo chamber. And although these sites occasionally conducted their own statistical studies, they mostly relied on existing academic work, giving political scientists an audience of unprecedented scale.

At the same time a movement was developing within political science to expand its reach beyond the ivory tower. In 2013 the American Political Science Association devised a plan to increase the field’s impact. Mr Drezner began advocating loudly for political scientists to publish papers on subjects where a consensus existed among the media and policymakers that was strongly refuted by academic literature. “We got tired of hearing people say things like ‘Values voters determine the outcome of this election’,” says Lynn Vavreck of UCLA. “We got tired of hearing things written into the history books that weren’t true.”

One group of professors who heard this message were the authors of TPD. Although their writing style does not quite qualify the book as a page-turner, TPD is essentially organised as a chronological narrative that is free of jargon and is sometimes outright funny. For example, it calls the share of delegates a candidate has won when a nomination is decided the “fat lady share”, in homage to the saying “It ain’t over ‘til the fat lady sings.”

The book’s argument is simple, convincing and provocative. Following the debacle of the Democratic convention in 1968, when police and street protesters clashed violently for days while delegates chose a pro-Vietnam-war candidate against the electorate’s wishes, America’s two major political parties introduced binding primary elections to let the public select nominees. But in the very first election cycle under the new system, Democratic voters made the disastrous choice of an anti-war insurgent, George McGovern, who went on to lose 49 of the 50 states to Richard Nixon. As a result, TPD claims, the parties soon set about undermining their own reforms. After a brief period of trial and error, they succeeded, maintaining a veneer of democratic legitimacy while all-but-inevitably guiding voters towards the preferred choice of party heavyweights and interest groups. “The reformers of the 1970s tried to wrest the presidential nomination away from insiders and to bestow it on rank-and-file partisans,” the authors write. “But the people who are regularly active in party politics have regained much of the control that was lost…Insider control is not unshakable, but it has usually been sufficient to the task at hand for some two decades.”

The arrow of causality

TPD backs up this claim with resounding evidence. For every contested primary between 1980, when the authors believe parties recovered their power over the process, and 2004 they measure the relative effect of polls, endorsements, fund-raising and media coverage on candidates’ delegate shares. Although successful candidates tend to fare well on all these indicators, the authors find that endorsements—their preferred measure of party support—are the best single predictor of delegate-winning. More important, early endorsements tend to yield cash, news coverage and popularity later on. In contrast, an early fund-raising push, media bubble or poll surge does not usually produce a flurry of endorsements. They conclude that parties tell the electorate how to vote, rather than voters telling the party whom to support.

When TPD was first published on the eve of Mr Obama’s election, it had virtually no impact on American politics. It was not until 2011, after Mr Silver cited the book in an article in the New York Times Magazine and the Republicans’ “invisible primary” to challenge Mr Obama was in full swing, that the public began to take notice: a look at Google searches reveals no significant interest for the phrase “invisible primary” before Mr Silver’s article. By May 2012 “invisible primary” had caught up with a well-known term like “efficient markets hypothesis” by search volume. And just when awareness of TPD was growing, its thesis was bolstered by an extraordinary performance. From the summer of 2011 until the Republicans’ South Carolina primary in January 2012, a parade of candidates with no support from the political elite (Michele Bachmann, Herman Cain and Newt Gingrich) took turns leading the polls. In the end it was Mitt Romney—whom many non-quantitative journalists dismissed as too moderate and establishment-friendly for an angry Republican electorate, even though he led the race for endorsements early on—who waltzed to the nomination.

So three years later, when a clownish insurgent called Donald Trump leapt to the top of the Republican polls, data journalists had their ammunition ready. In a story last July entitled “Here’s Why He Won’t Win”, Andrew Prokop of Vox predicted it would be hard “for candidates like [Mr Trump] to appeal to party elites”. “Dear Media, Stop Freaking Out About Donald Trump’s Polls” was the title of a piece in November by Mr Silver. “Donald Trump…will most likely follow the classic pattern of a party-backed decline,” concurred Nate Cohn of “The Upshot” in July. And we wrote in late September that “Outsiders don’t win presidential nominations any more…barring a stunning reversal of precedent, [Mr Trump’s] failure to impress GOP elders…all but precludes [him] from becoming the party’s flag-bearer.” In a daily reminder to readers that Mr Trump’s bubble was sure to pop, “FiveThirtyEight” has paid homage to TPD by maintaining an “endorsement primary” tracker, which is updated each time a senior elected official announces support for a candidate. After Mr Trump’s poor showing in Iowa, such observers had reason to feel smug.

One month later, however, it seems clear that Mr Trump is no Herman Cain. The first panic bells went off after his dominating performance in the New Hampshire primaries, which occurred in tandem with Bernie Sanders’s trouncing of Hillary Clinton, the establishment favourite. (“Bad Night for ‘The Party Decides’,” Ryan Lizza of the New Yorker tweeted as the polls were closing.) Mr Trump’s thumping win in South Carolina forced Jeb Bush, the original leader in the Republican “endorsement primary”, out of the race, setting off a new wave of sober predictions that the party would now clear the field for Marco Rubio to eviscerate Mr Trump one-on-one. Then came Mr Trump’s 22-percentage-point win in Nevada, his victories in seven of the 11 Super Tuesday states and the continuing division of his opposition. Since late February the very Republican governors and senators who previously swore he had to be stopped have begun to offer him their endorsements. There isn’t much time left for TPD to be proved right. What good is political science if it flubs the biggest development in American politics in generations? The authors of TPD themselves are responding cautiously to what might look like humiliation. Martin Cohen, of James Madison University, plaintively maintains that the book’s statistical model has actually held up rather well. TPD did include a crucial caveat in its argument: “The party and not individually powerful candidates decide nominations—but only if the party can make up its collective mind.” TPD found that a high share of early endorsements usually leads to the nomination. Although Hillary Clinton was widely considered the insider favourite in 2008, her endorsement totals on the eve of the Iowa caucuses lagged far behind her husband’s at the same stage in 1992 or Al Gore’s in 2000. Meanwhile, TPD’s authors noted that Mr Obama, the eventual victor, had already amassed a healthy share of endorsements from low-level party insiders. This year, Mrs Clinton really has been the overwhelming endorsement leader, and looks set to cruise to victory. In contrast, among the Republicans in 2016, no candidate received significant endorsement support by historical standards. Mr Bush, the endorsement leader, had 30% less backing from the party ahead of the Iowa caucuses than the lowest previous total on that date by an eventual Republican nominee. “The party really didn’t decide,” Mr Cohen says, “and as a result it was left to the voters.” Yet Mr Cohen is not hiding behind this technicality. “We think that it’s in the party’s interest to decide, and that they should be deciding,” he says. “The fact that they failed to is a lack of foresight on their part.” Even if TPD’s statistical model is sound, its central claim—that American political parties have successfully “beaten” the reforms intended to entrust nominations to the electorate—is hard to reconcile with Mr Trump’s winning streak.