As America ticks down the days until Donald Trump leaves Washington, it seems incumbent on those of us who’ve gritted our teeth and downed our bourbons through this never-ending cold-sweat fever dream of a presidency to try to explain—not for the last time, to be sure—what, if anything, this four-year spasm of discontent adds up to. Is there a Unified Field Theory that extracts meaning from the wild barrage of scandals and controversies, mendacity and meanness, hate-mongering and vainglory, that has pumped up everyone’s blood pressure since November 2016?

So far, surprisingly, overarching analyses of the Trump administration have been scarce. Instead, we’ve made do with laundry lists and inventories detailing the president’s “worst” or most “unthinkable” deeds. That may be because the sheer chaos of Trump’s high-decibel White House sojourn—the exhausting fusillades of rhetorical warfare and moral indignation—has confounded any sober efforts to take stock. News coverage and social media reaction have lurched from moment to moment, outrage to outrage, tweet to tweet, invading the quiet terrain where reflection and understanding flourish. In fact, if Trump’s presidency can be said to have a defining quality, it might well be chaos itself.

As a card-carrying historian, I realize it’s premature to try to pinpoint Trump’s place in the sweep of history. What comes next will be as important as what has come so far. But having studied the presidency, past and present, for most of my adult life, I can’t help thinking that that chaos—or, more precisely, the deliberate breakdown of rules—is what Trump’s presidency was all about.

That might sound like a stylistic critique. After all, Trump’s presidency was also marked by a crude ultra-populist politics, as seen in such features as his atavistic “America First” foreign policy, his determination to halt illegal immigration, including through morally and legally dubious methods, and the surge in overt expressions of racism, like the 2017 Charlottesville rally. But those Trumpian developments are actually connected to the president’s assault on America’s rules and norms. Under a healthy political order, demotic feelings that are ugly, undignified, cruel and violent are kept under control by a whole pyramid of habits, institutions and models of behavior. In both style and substance, Trump took a sledgehammer to that pyramid—and survived with a stronger base of support than anyone predicted. His flouting of the laws, institutions and precedents that had made the United States (for the most part, at least) an exemplar of democracy in the eyes of its citizens and abroad was the ground from which so much else about the Trump presidency springs. It will be taking its toll on our politics for some time to come.

Consider: The petty public insults thrown at world leaders, judges and his own Cabinet members. The brazen comfort with nepotism and self-dealing. The casual mendacity. The imperious browbeating of journalists. The shameless solicitation of foreign actors to meddle in U.S. elections. The refusal to concede the 2020 presidential race long after his defeat was apparent. And his role in the event that right now overshadows almost everything else about his tenure in office: his instigation of the seditious riot at the U.S. Capitol on January 6. Trump’s signature move through all of this has been the snubbing of his nose at the canons that others would have him follow. Even his physicality expresses his hostility toward basic civility: shoving aside the Montenegrin prime minister at a 2017 NATO meeting, stalking Hillary Clinton in the 2016 debates (and madly interrupting Joe Biden in the 2020 contests), storming out of an unfinished “60 Minutes” interview because he didn’t like the questions.