What about patterns of actual individual behavior? After all, policy and guidance go only so far.

If you recall the endless social media videos of arguments over masking policies in Walmarts and Whole Foods, it may be hard to believe that surveys show only a small partisan gap on the issue through 2020. And yet, according to a large survey conducted by Pew in August 2020, 92 percent of Democrats said they had worn a mask when in stores and other businesses all or most of the time over the previous month, and 76 percent of Republicans said the same. (The gaps widened considerably over the next six months.)

Somewhat creepily, you can also track the actual social behavior of people through cellphone data, as well. In the summer of 2020, according to Google’s mobility data, the states with the biggest declines in retail activity were, in order, Hawaii, California, New York, Florida, New Jersey, Arizona, Massachusetts and Texas. By the fall, the biggest declines in grocery activity were in Hawaii, Florida, California, Arizona, New Mexico and Texas — and the overall impact, across all 50 states, was less than 4 percentage points below prepandemic levels of activity.

So what happened? How was pandemic unanimity transmogrified into perhaps the clearest illustration of our self-destructive culture war?

First, there was, you might remember, a presidential campaign, with the challenger faulting the incumbent for the pandemic’s brutality and the incumbent claiming it was all no big deal.

Second, there was simple exhaustion over mitigation policies — closed schools, limited socialization, suspended professional and family and romantic life — with each party offering different perspectives on how to put the previous six months behind us.