Trump is probably the best thing to ever happen to the Democratic Party since FDR and JFK. If anything, they should pray that he wins in 2020. 2022 would be a Republican bloodbath with the Dems likely to attain near-supermajorities in Congress and over 30 governorships (plus the majority of statehouses).
But it would be terrible for America. We would probably end up with a level of political rancor not known since the Civil War. We would have civil unrest characteristic of that just before the Civil War. Conspiracy theories on the Far Left would be as nasty as those on the Right today.
Nobody would believe anything as the American political system solves nothing but tempers heat up. Maybe there would be outright domestic terrorism with plenty of targets.
Count on Trump having purged the FBI of anyone not a Trump supporter, and as much as an 8-1 split in Supreme Court decisions (Sonia Sotomayor is the sole dissenter) that are unpopular with sizable majorities. Donald Trump has no legal training and no respect for legal precedent. Consider how President Obama prepared America for
Obergfell -- he could predict which way the ruling would go based on state-by-state patterns, and he got Americans to prepare themselves for the ruling once it applied to all fifty states and US territories.