Already, this is too easy to forget.
We've covered that Republican turnout was actually low. Not by much, but slightly below trend. Meanwhile Democratic turnout -- although not high enough to win the crucial red states -- was fairly good nationwide, if down somewhat from the previous peak. It just wasn't quite good enough in a few keys states. Why? Was there some winning over of voters on a policy issue? No, most folks who voted stuck to their usual party. So how did it happen? Largely, the voter data shows it hinged upon that just barely enough-to-swing-it previously Democratic-leaning voters didn't vote in 2016. While voter data alone can't tell us exactly what drove that swing, it shows that the question of the election was what kept just the critical number of voters in the key states from showing up.
Aside from rather successful Republican voter suppression efforts with voter ID laws, Matthew Yglesias performed a solid analysis of how the story rolled. In short, it was the emails. As Yglesias puts it, "Indeed, research from Gallup indicates that emails dominated what voters heard about Clinton all throughout the campaign."
That's it. That's ultimately the issue on which the 45th Presidency turned. The choice of which email server to use. Not jobs. Not healthcare. Not taxes. Not immigration. It's the emails.
Yes, arguably, the Democrat's candidate might have been able to win despite the email issue had she been more charismatic, better able to inspire even more people to look at her carefully developed set of sensible policy approaches. That it was the emails does not defend the performance of the candidate who merely won the popular vote. While the campaign platform may have been solid and the campaign pitched those policies enough to earn a sizeable majority of the popular vote nationwide, the 2016 Clinton campaign failed to make it about all those thoroughly thought-out policies in enough states. Crucially, she failed to make it not be about the emails in key swing states.
But any "might have" doesn't change what it was about. Where the votes counted, it was about the emails. If there was anything the 2016 election can be said to be about: the overriding mandate from the electorate was, "do not use a private email server as a public servant".
Let's not forget that. No matter how tempting it might be to forget.
Meanwhile, if there's a lesson for future campaigns, it would seem to be this: pick a candidate far too charismatic to have their message drowned out by some flap about what server they used for their email.