There is really excellent analysis here. Such as: "Some still maintain that rising education levels and growing minority populations ensure future Democratic majorities. But Republicans keep winning elections, even in places like Maryland and Massachusetts where these trends are most advanced. And in a Trumpian future of voter suppression, gerrymandering, and sundry other assaults on democracy, it will take much more than 51 percent support to reverse policy directions."
An interesting exercise: Find an online list of states by per capita income. The richest states pretty much correlate with the Democratic bicoastal voting bloc. Minnesota and Illinois were the breakpoint - the lower states caved in. Obama didn't bring the rest of the country affluence, and Clinton had no clear message for those still struggling. The recession was very slow to leave NM, and then oil revenues tanked. Tourism is up, but the rest is treading lukewarm water, in fear of the next crunch.