We thought it could never happen. That’s what happened.

I’m listening to Hillary Clinton’s book on my commute. Its publication brings back the usual debates about how Donald Trump was able to win the Presidency, given his obvious, comprehensive unfitness for the position.

How did that happen? When I was asked to give odds before Election Day, I always quoted Nate Silver’s estimates. I said there was a one in six chance Trump could win.*** In my bones, I never really believed the risk was that great. Most people I knew-with the notable exception of Keith Humphreys-felt the same way. That’s how it happened.

The biggest single factor in President Trump’s upset election victory was the collective sense that Hillary Clinton couldn’t possibly lose. That conviction in our bones-that the unthinkable outcome was really impossible-freed everyone, across the political spectrum from doing their part to prevent the national catastrophe that actually ensued.

That complacency freed unenthusiastic voters who despised Trump to stay home or cast protest votes. It freed Clinton and her team to run a less-urgent, less-effective campaign than they might have been. It freed Bernie Sanders not to do everything he might have done to rally his supporters on Clinton’s behalf.

It freed the media to cover her as the presumptive President, to ridiculously over-hype the email scandal, to treat Trump as a clownish and entertaining side-show, to give him free air time, to hire dishonest Trump spokesmen as cable news talent, to take refuge in bromides about the two-party duopoly and both-siderism. Hillary Clinton deserved criticism and scrutiny on many fronts, particularly her decisions regarding the lucrative speeches. She is absolutely, absolutely correct to lambaste the New York Times, Matt Lauer, and other media outlets for terrible and consequentially biased campaign reporting.

That same complacency freed folk on the left to snipe at her without worrying that this would influence the contest. It freed many in the political right and center to avoid mobilizing around Hillary although they knew perfectly well that Trump was a threat to the nation. It freed President Obama to be less aggressive than he might have been in addressing Russian interference in the election. It freed FBI Director Comey to behave as he did, excessively upbraiding Hillary Clinton even as he (perhaps appropriately) shielded much more serious investigations of the Trump team from public view. It freed all of us to be more passive and not to do as much as we might have done to help her when things got close.

As it turned out, most of us overestimated the impact of Trump’s comprehensive unworthiness to impeach him among key Republican-leaning voters. We underestimated the impact of Trump’s racism, sexism, and other bigotries to specifically validate him within another key group of Republican-leaning voters that was larger than many of us expected.

That left a hole, not as deep as a well nor so wide as a church-door, but enough.

***Dina Pomerantz reminds me over Twitter that Nate Silver on Election Day had given Donald Trump an almost-thirty-percent chance of winning. Indeed Silver and the Atlantic’s Ron Brownstein anticipated with great insight precisely the dangers Clinton faced in the battleground states. I would tell people one-sixth because I believed the hype that Clinton’s campaign possessed superior analytics and a better ground-game. Ah, those were the days.