In my opinion it COULD be a nightmare scenario if it causes passions to ignite, or it could be a wakeup call that radicalism of any sort is ultimately self-defeating. If the Democrats realize that galloping to the hardest edges of the Left rather than sticking with mainstream liberalism is a losing proposition, then they may correct course, much as Republicans long ago realized that they needed to jettison their crazies (the John Birch Society anybody?).
What is going to be interesting is the growing amount of evidence of how popular Trump is in various minority communities, especially amongst African-Americans. For generations Democrat leaders have promised those communities the sun, the moon, the stars, and various other celestial objects in exchange for their votes... and never bothered to deliver. Trump said that his policies and actions would benefit the various minority communities in concrete, measurable ways... and delivered (black unemployment is at record lows, for one thing...). Everytime Trump goes to bat for some minority person being persecuted (which he's done regularly) he further illustrates that the institutional left is either incapable of dealing with the issues facing minorities... or simply unwilling to do so.
My hope is that people rediscover the lost art of disagreeing with the substance of a person's ideas, without attacking the person. My wish is that we realize that neither the left nor the right have a monopoly on truth, that neither liberals nor conservative are ipso facto monsters to be destroyed but fellow citizens to coexist with and persuade.
What gives me hope is the realization that for all the sound and fury of the modern age, most of the discourse is actually (on a historical basis) quite tame. That the invective and vitriol of the debate is not even close to rising to the level of personal vitriol and venom of the past. So long as we are willing to debate with words, not swords, I think we'll ultimately be fine. I just pray that nobody, on either side, decides to flip the equation.
EDIT - typos