But for the better part of the 20th century, most Americans considered themselves Democrats or Republicans and, depending on the political climate, often crossed over at the polls. Each party represented a certain overall worldview: the Democrats pro-labor, economic reform, social safety net, and progressivism; the Republicans fiscal discipline, smaller government, individual responsibility, libertarianism, and traditionalism. Within these strictures there was considerable flexibility. The other side’s position might be seen as wrong-headed but it wasn’t anathema. The operative word was “consensus”—respecting the other party’s position and hammering out a compromise in an atmosphere that, for all its cantankerousness and bombast, was still congenial. Most politicians and their adherents stayed within bounds. One ventured beyond them—as did Senator Joseph McCarthy—at his own peril. Rather, politicians would declaim the disabilities of the opposition, or even joke at the foibles of their own side. As the humorist Will Rogers famously observed: “I belong to no organized party. I am a Democrat.”

It wasn’t until fairly recently that Democrats were turned into leftists and Republicans into rightists. These are terms of mutual abuse. Not only are they foreign imports but, worse, they tar their targets with the brush of foreignness. If you’re a Democrat who supports more liberalized immigration policies or a woman’s right to choose or the Affordable Care Act, you are a leftist, an alien whose beliefs will undermine the country. At best you are a useful idiot if not an outright traitor. If you are a Republican who advocates tighter immigration, more religion in the public weal, gun rights, and fewer taxes you are a rightist.