You do realize that the Democratic edge with 18-29 year-olds was literally cut in half between 2012 and 2016, right? It seems that that generation is already moving back towards the center. Let's see how the 18-29s vote in 2020 (I expect a single-digit margin).
What?
Obama '12: 60 - 37
Clinton '16: 55 - 36
That's not half. Hillary lost 5 points and Trump actually did a point worse than Romney. That's not moving back to the center. I'd venture a guess her drop in support was mostly due to Hillary being Hillary - Millennial disdain for her was bound to cost her something. Also worth noting here is that Hillary did even better (and Trump worse) with 18-24 year olds, 56 - 34. That's fking terrible for the GOP.
Gary Johnson and Jill Stien. Even my sister in law refused to vote for Hillary and voted for Bernie instead. A lot of very liberal people were almost indistinguishable from Trump sometimes on my fb feed. Just look at Shadows.
The main issue is how to turn out both the very Democratic and the kinda Democratic.