Fully 12 percent of people who voted for Sen. Bernie Sanders, I-Vt., in the 2016 Democratic presidential primaries voted for President Trump in the general election. That's according to the data from the Cooperative Congressional Election Study a massive election survey of around 50,000 people. (For perspective, a run-of-the-mill survey measuring Trump's job approval right now has a sample of 800 to 1,500.)
What drove those voters to Trump? Schaffner dug into that, as well. What it wasn't was trade, an issue where Sanders was closer to Trump's philosophy than Clinton's. At least, the issue of trade didn't seem to have that much of an impact.
Party seems to have had something to do with it Sanders-Trump voters were much less likely than Sanders-Clinton or Sanders-third-party voters to have been Democrats. Likewise, approval of President Barack Obama appears to be related Sanders-Trump voters approved of Obama much less than other Sanders primary voters.
And then there's race. Nearly half of Sanders-Trump voters disagree with the idea that "white people have advantages." That's much higher than the share of other Sanders voters who agreed with that idea.
To answer the question many Clinton supporters may be asking: By this data, yes there are enough of those Sanders-Trump voters to have potentially swung the election toward Clinton and away from Trump.
Specifically, if the Sanders-Trump voters in Michigan, Wisconsin and Pennsylvania had voted for Clinton, or even stayed home on Election Day, those states would have swung to Clinton, and she would have won 46 more electoral votes, putting her at 278 enough to win, in other words.
More info about it here.
Blame anyone but Hillary Clinton if old.