If some major conspiracy was under way, I'm not sure Facbook, Google, Twitter censorhip alone would be enough to stop it?
American elections have become so polarized that 50 000 votes in strategically important states can swing them.
It is definitely in capabilities of the tech giants to effect such a small change by putting their thumbs on the scales.
Of course, this is a general problem with the "winner takes all" political principle, and already the ancient Greeks knew that problem, but given that you can't have two Presidents at the same time, it is hard to avoid.
Even European countries where the President is usually just a figurehead suffer from bitter polarization when it comes to presidential elections.