For all Mueller’s probity, this investigation has an inescapable political destination. Mueller must refer any evidence of wrongdoing by Trump himself to the House of Representatives as evidence of possible “high crimes and misdemeanors” that might warrant impeachment. Would this GOP-dominated House begin impeachment proceedings, even on strong evidence of obstruction? Right now, you’d have to guess no.

The real collision point ahead is the 2018 midterm election. This will be the “impeachment election,” and it may be as bitterly contested as any in decades. Trump seems unlikely to take Nixon’s course of resigning before the House votes on impeachment. He’ll fight all the way — a combative president trying to save his mandate from what he has described as a “witch hunt.” This appeal would resonate with a populist base that already feels disenfranchised by jurists and journalists.

As Mueller proceeds with his investigation, the world of Washington needs to be level-headed. The politics of polarization is only beginning. Trump’s war on the media and its sources will get nastier. How do citizens hold Trump accountable without the process seeming like vengeful payback from media and political elites? Graham Allison, director of Harvard’s Belfer Center for Science and International Affairs, notes that elite opinion may already regard Trump as “unfit for office,” but he cautions: “When I contrast this with what many fellow citizens believe about elites, yikes.”