Democrats Lost Because Democrats Didn't VoteMany stories have been written (and are yet to be written) about why Hillary Clinton lost. Economists like the idea of "workers are hurting badly" (although see below). Social scientists would probably prefer the "there are a lot of racists out there" line. We're data nerds, so we have a different angle: Democrats didn't bother to vote this time. We even have a downloadable Excel spreadsheet to help make our case. Here are the data from the spreadsheet:

It's a big chart with lots of little numbers, so where do we start? The second and third columns are the Clinton and Trump raw vote in 2016. The fourth column is Clinton minus Trump, so positive means Clinton won the state and negative means Trump won it. From the bottom line we see that Hillary Clinton won the national popular vote in 2016 by 282,546 votes out of a total of 119.8 million votes or 0.2%. Trump's margins in Michigan, Wisconsin, and Pennsylvania were 11,837 and 27,357, and 68,236, respectively. If Clinton had gotten 107,430 more votes in these three states in the right proportion, she would have won the election. In other words, a change of less than 0.1% of the vote, properly placed, would have flipped the presidency. A Trump surprise it was, but a landslide it was not.
Columns five through seven are the analogous data for 2012. Column 8 is how many more Democrats voted in 2016 compared to 2012 as a percentage of the 2012 vote. So for example, in Washington 30.42% fewer Democrats voted for Clinton than voted for Obama in 2012, despite the U.S. population being over 3% larger in 2016. Washington Democrats, you are not doing your job. Column nine is the same thing for the Republicans. Here we see that North Dakota Republican turnout was 14.86% higher in 2016 than in 2012. North Dakota Republicans, you are performing your civic duty very well, congratulations.
Now, let's go back to the bottom row again. In 2016, 60.1 million Democrats voted, compared to 65.9 million in 2012, even though the population was 3.5% larger this year. That's a huge drop-off. In contrast, Republican turnout was down only slightly, from 60.9 million to 59.8 million this year. So our first conclusion is that the Democrats lost because 6 million fewer of them voted this year than last time.
The next question is, where did the dropoff occur? Was it, for example, largely in red states that have adopted stricter requirements to vote? The first thing we note is the champions in not-voting were Washington and California, two very blue states. The table is sorted on column 8, so we see the state where Democratic turnout improved the most is—Texas. What about the states that Obama won but Clinton lost? These are marked in orange in the last two columns. In Iowa and Ohio, Democratic turnout was way down and Republican turnout was somewhat up. Neither state had serious voting restrictions. The Democrats have only themselves to blame. If as many Democrats had voted in Ohio as in 2012, Clinton would have carried the state by over 100,000 votes. Wisconsin and Michigan have similar stories. If Clinton's turnout had matched Obama's, she would have won both states easily.
Pennsylvania is different. There, Democratic turnout didn't fall too much, but Republican turnout was up almost 9%. Finally, in Florida, we have one of only five states where Democratic turnout was better than in 2012 (and only three where it was higher when you correct for population growth). Unfortunately for the Democrats, Republican turnout improved by even more than Democratic turnout.
So, our conclusion is that Democrats lost because their turnout was down, rather than because millions of new Republicans suddenly decided to vote. What we can't see is why. In some cases, it could be due to restrictive state or local laws, in others it could be because supporters of Sen. Bernie Sanders (I-VT) decided both Clinton and Trump were corporate stooges and there was no difference between them. Maybe other reasons. We'll leave that for others to figure out. (V)