Which brings us back to television — and in particular, the rise of partisan cable like Fox News and MSNBC. A recent analysis using large-scale data identifies cable television news as a major contributor to polarization. This narrative arguably fits with the timing of the rise in interparty animus, and it is consistent with the rise in polarization among groups — such as the elderly — with limited internet use but high rates of television viewing.

We would also look to the behavior of politicians and the parties. Data from congressional roll-call voting show that the increase in polarization in the Senate and House started well before it can be detected for voters, and though elected leaders follow their constituents much of the time, they can also lead them. Today the parties seem to speak different languages, with Republicans talking about “illegal aliens” and “the death tax” while Democrats talk about “undocumented workers” and “the estate tax.” An analysis of the Congressional Record that Gentzkow and Shapiro conducted with the statistician Matt Taddy finds that this linguistic rift opened up right around the time of the Contract With America, when the Republican leadership adopted a successful strategy of using wordcraft to frame the issues of the day.

Where we suspect the most important causes lie is in the deeper structural changes that have caused the experiences of those in the red and blue parts of the country to diverge. A voter’s party identification is increasingly related to his or her position in the income distribution, with the top quintile containing disproportionately more Republicans. At the national level, income inequality and polarization in Congress track each other closely. Furthermore, congressional districts that were adversely affected by the rise of Chinese imports have been shown to elect less centrist representatives from both parties.

The social-media-as-villain narrative is gripping because it plays vividly to our fears. But that is not the only reason it holds such sway. It also lets us collectively off the hook. Why are half of Americans thinking and acting in ways the other half cannot comprehend? Why did one of those halves choose Donald Trump to be their president? Easy, the social media narrative would say: They were brainwashed. They were duped by the bad guys — fake news or Russian robots or big-data-driven algorithmically targeted psi-ops propaganda.

At some fundamental level, they don’t really mean what they are saying, and if only they weren’t so gullible or so vulnerable they would see things our way. To find solutions we don’t need to look at our own behavior, or values, or consumption patterns — we just need to beat the bad guys at the gate.

As tempting as that story is, it is at best incomplete. Like many inflection points in history, this one was probably not caused by any single change, but by the fact that many important changes happened to converge at the same time. The factors that likely matter the most are those that have caused the real experiences of Americans to diverge.