How did it happen? We can get into swing state demographics and electoral college math but the surprising truth is in the totals (as of 12/19/2016):
This post has been updated as the final 2016 totals have come in. At first it appeared Donald Trump didn't win any more votes nationwide than Mitt Romney, but now it's clear that by a small margin he got the most votes ever for a Republican. Trump won in 2016 with 3 million more votes than McCain in 2008, 2 million more than Romney in 2012, and only .9 million more than Bush in 2004.
There's also a drop of 3.7 million Democratic voters since 2008. We'll call them the disillusioned. Some of them may have become deplorable Trump voters, but it would appear that a lot of them ran to the third party candidates. No more than 74 thousand Obama 2012 voters stayed home and voted with their seat.
I'm not saying angry Hillary voters should run out and slash the tires of cars with Bernie bumper stickers, punch Jill Stein supporters in the nose, or break into homes that had Gary Johnson yard signs and steal their stash, although that might help ease the pain.
Defriending Republican-voting friends on Facebook also isn't going to help. They're not the cause. They didn't do anything more than Republicans always do, vote Republican, and not in any great numbers. Nor are the ranks of the disillusioned who didn't vote for Hillary Clinton burning American flags on Fifth Avenue in NYC going to win over Americans to vote Democratic in the next election.
Blame the candidate, but the trend was there in 2012 too. It's The Incredible Shrinking Democratic Party.
If you're looking for a bright spot, there is one. Hillary polled 18.4 million votes more than her husband Bill ever did. So, for women, that's a moral victory. She also polled higher than George W. Bush.