How is Facebook going to "prevent" a Trump Presidency? Censorship? Biased coverage? Free political ads for his opponent?
Facebook as a company should stay out of it and let the democratic process work. Everyone who supports a losing Presidential candidate has to accept the will of their fellow voters, whether he's an odious, obnoxious boor or not.
If you, as a person, don't like Trump, volunteer for the campaigns of his opponents and vote against him. Don't leverage your status as a Facebook employee to suppress democracy.