People seem to want to point the finger at one thing and one thing only, but guess what... something this big and complex isn't going to have 1 simple cause...Factors that ALL contributed to Trump being elected include (in no particular order)...
1. DNC Meddling
2. Bernie not conceding soon enough despite the DNC meddling.
3. A largely bs email investigation.
4. A separate email hack by Russians.
5. Fake news and other propaganda spread by Russians.
6. Fake news and other propaganda spread by for-profit right wing sites.
7. Hillary's "Trust Issues" (whether or not you think those were justified or not).
8. Our shitty electoral college system that gives smaller/less populous states more weighting in the system. Remember...the major of americans, by 2.8 million, voted for H.
9. James Comey's dumbassery.
10. *****TRUMP VOTERS***** (sub-causes: a racist, xenophobic voter base exercising backlash and racial resentment over 8 years of a black left-of-center president).
I'm sure I could think of 10 more if I tried. The point is, if any ONE of these things didn't happen, the outcome may have been different, but that doesn't mean whatever ONE thing you choose to cherry-pick was some sort of "ultimate cause".
In short, this election was a cluster-fuck.