In America today, there are conservative and liberal jeans (Levi Strauss versus Wrangler), liquor (Heineken versus Coors), and footwear (Birkenstocks versus cowboy boots). The MAGA movement itself is seen as tied to Kid Rock and eating steak.

In an era when partisan division is so febrile that acceptance of political violence has grown and violent political attacks are on the rise — the Charlie Kirk assassination being the latest of great note — it is hard to remember that it wasn’t always so.

As recently as the 1950s, Americans were politically calm — so calm that a committee of the American Political Science Association urged the two parties to accentuate their differences, to provide a “true choice.” In 1964, Barry Goldwater campaigned for president as the Republican who would provide “a choice, not an echo” and was badly defeated for his pains. Some political scientists applauded the political apathy of the era as both a sign of popular satisfaction and a shock absorber for the system. Four generations on, there seems to be too much party difference and too little political apathy.

Why have we gotten to a place where even open-toed sandals are left-wing?

Simple answers might point to combative politicians, President Donald Trump above all, to aggressive social movements like the Tea Party and Black Lives Matter, or to changes in the media such as the rise of cable television and then online feeds like Facebook and TikTok. But the key dynamic, many researchers have found, is the increasing proportion of Americans for whom political affiliation is central to their identities — to what they think, to what they feel, to who they feel they are.

I need to stop right here: This assertion does not directly apply to most Americans. In 2024, only 30 percent of Americans described themselves as “strong” Democrats or Republicans (only about half even claimed a political party). The largest chunk of Americans are not partisans. About politics, they care little, talk little, consume little, and know little — and they vote little (although when they vote they determine who holds power, the partisans being evenly divided).

Politicization has now gone beyond shaping many Americans’ stances on issues or even their cultural tastes, to shaping who they are.

Still, the politicization of so many Americans matters even for the apolitical. The latter are the audience for the political theater — which Americans find “exhausting” — and when they do vote, usually only every four years, they are presented with polarized options. For the nation as a whole, it means less constructive cooperation and more animosity and anger.

A different story of political polarization

There is a story of political polarization that has often been told. Differences between the national parties were narrow in the first half of the 20th century. A higher percentage of Republican than Democratic senators voted for the 1964 Civil Rights Act; 13 Republican senators voted in 1965 to establish Medicare.

Then the division between the politicians widened greatly and quickly, first probably driven by racial issues and then by others. When Obamacare passed in 2010, it did so with zero Republican votes; only one Democrat voted for the Supreme Court appointment of Justice Brett Kavanaugh in 2018. The widening chasm spread to other areas of government, for example, to state legislatures and judicial decisions, and on to the politically engaged public.

Party has become so important that opinions on how much racial discrimination exists now differ more between Democrats and Republicans than between Black people and white people.

But politicization entails much more than the parties dividing on policies. Politicization has now gone beyond shaping many Americans’ stances on issues or even their cultural tastes, to shaping who they are — whom they date (and marry and befriend), what........

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