Once upon a time, Prime Minister David Cameron sat down at a pizza restaurant at O'Hare and made the decision that would later destroy his career: To quiet the right wing of his Conservative party, he would allow a vote on a referendum for the United Kingdom to exit the European Union. It would fail; Cameron would retain power; life would go on.

(If Cameron quietly munching deep-dish among the hoi polloi while plotting a Wile E. Coyote electoral maneuver seems farfetched, Kim Janssen reports that his route from the airport to the NATO summit avoided the terminals. Still, why not print the legend: Churchill at Yalta, Keynes at Bretton Woods, Cameron at the airport food court.)

It didn't fail; Cameron is stepping down; and there's chatter that Ireland could reunify and, along with Scotland, leave the UK for the EU. As Cameron's Conservative colleague David Lidington put it, "it was like Balrog waiting to be awakened."

The Brexit and the continued persistence of Donald Trump has kept a piece by the University of Chicago economist Amir Sufi on my mind. Along with Princeton's Atif Mian, he wrote House of Debt, a forensic accounting of household debt's role in the Great Recession, which I talked to him about in 2014.

Around that time, Sufi, Mian, and Francesco Trebbi also collaborated on the effect of financial crises on political polarization. What they found is, well, maybe not surprising:

Polarization in Congress has increased steadily over the past four decades, but our research suggests that it rose more sharply after banking crises and market crashes. And this pattern extends beyond the U.S.: after financial crises, polarization among voters was common across all 70 countries sampled in the Reinhart-Rogoff data set.

[…]

Our conclusion: financial crises tend to radicalize electorates. After a banking, currency, or debt crisis, our data indicate, the share of centrists or moderates in a country went down, while the share of left- or right-wing radicals went up in most cases.

The divisions over the Brexit are more complex than right-versus-left. The austerity politics of the European Union raised opposition against it within Britain. Take Owen Jones, the young social democratic writer and activist, in the Guardian last year, arguing for an exit:

As austerity-ravaged Greece was placed under what Yanis Varoufakis terms a “postmodern occupation,” its sovereignty overturned and compelled to implement more of the policies that have achieved nothing but economic ruin, Britain’s left is turning against the European Union, and fast.

In the piece, he cites George Monbiot, addressing something that should sound familiar to Americans:

I accept the principle that the EU should represent our joint interests in creating treaties for the betterment of humankind. I do not accept that it has a right to go behind our backs and quietly negotiate a treaty with the U.S. – the Transatlantic Trade and Investment Partnership (TTIP) – that transfers power from parliaments to corporations.

And Suzanne Moore (ditto):

If the European project that once seemed so noble now comes down to the European Central Bank, which is not in any way independent but acts as a thuggish bailiff to further impoverish Greece, what actually is it? If Germans believe they should not have to pay for the mistakes of Greek governments, then they do not see the crisis of Greece for what it is: a crisis of all Europe. Bailouts have been funded for the financial sector since 2008. To simply blame Greece is unsustainable.

They all acknowledge that the Brexit is associated with a reactionary anti-immigrant movement, and wrestle with the difficulties of supporting it from a left-leaning perspective. You can see the same dynamic in the coverage by Jacobin, the American socialist magazine: the argument that the left has to support the Brexit because "it is not the case that everyone who supports Leave is a paid-up racist xenophobe who wants to stop migration," and that the EU is "brutal and undemocratic."

On the flip side, Ed Rooksby writes that "troubling fact is that while staying in the European Union is certainly a horrible idea, the prospect of withdrawal seems, as things currently stand, much worse," because "the existing Brexit campaign is led by reactionary and dangerous arguments, ideas, and political forces."

There are parallels to an American left, dissatisfied with what Hillary Clinton represents, figuring out what to do about the fact she's opposed by a reactionary anti-immigration candidate turned out by a fractured conservative party.

John Harris's dispatch from all over Britain could easily be swapped into American campaign coverage, down to the intersection of labor and geography:

In Peterborough in 2013, we found a town riven by cold resentments, where people claimed agencies would only hire non-UK nationals who would work insane shifts for risible rates; in the Ukip heartlands of Lincolnshire, we chronicled communities built around agricultural work and food processing that were cleanly divided in two, between optimistic new arrivals and resentful, miserable locals….

[…]

What defines these furies is often clear enough: a terrible shortage of homes, an impossibly precarious job market, a too-often overlooked sense that men (and men are particularly relevant here) who would once have been certain in their identity as miners, or steelworkers, now feel demeaned and ignored. The attempts of mainstream politics to still the anger have probably only made it worse: oily tributes to “hardworking families,” or the the fingers-down-a-blackboard trope of “social mobility,” with its suggestion that the only thing Westminster can offer working-class people is a specious chance of not being working class anymore.

What Sufi, Mian, and Trebbi find, again, is probably not surprising to many people who have followed American and European political history, recent or long ago. But they sound another warning—that the political results of fracture tend to create gridlock, and gridlock has the opposite effect of what populist insurgencies desire: "Political gridlock and lack of reform are natural outcomes of polarisation [sic]. Gridlock delays reform and possibly makes recovery slower (explaining the long recessions and sluggish recoveries)."

It's also evidence that such warnings go unheeded by dominant, relatively centrist elites, over and over again, to their political detriment:

This extreme polarization is in line with our conclusions and those of a subsequent paper by three German scholars who studied 800 elections in 20 countries between 1870 and 2014. [They] identified the extreme right… as the principal political beneficiary of postcrisis partisanship.“Voters seem to be systematically lured by the political rhetoric of the far right, with its frequently nationalistic or xenophobic tendencies,” they write. Overall, they conclude, “the political effects [of banking and financial crises] are particularly disruptive.”

The immediate reaction in the United States has been to try to figure out what the Brexit augurs about the presidential election. But in some ways the parallels are already here and have been with us for awhile—increased polarization and gridlock, and not just at the national level, which exacerbate the problems the polarization is intended to address. If the powers that be want to avoid a reactionary revolt, they have to figure out policies that aren't merely reactive.