I don't believe that the occurrence of an election is itself causation at work.
The reason it seems that way, to me, is the same reason that abused women tend to step out of their shame when they see other women doing it, or when their anger is kindled into a flame that exceeds their fear. People feel empowered when they realize they're not alone (edit: and someone they identify as a peer has given a voice to their own beliefs, experiences or feelings)
Sometimes, that feeling of empowerment makes them speak up. Sometimes it makes them lash out. It's an unfortunate coincidence that a presidential candidate is directly responsible for catalyzing both groups of people into responding so passionately today.
Realistically, I believe that the electorate has felt disenfranchised (using the more general "deprived of a voice" definition) for many years now, and for various reasons. A republic such as ours can never have an electorate that, in its entirety, feels like their voices are heard. I don't know how to help that; I don't think anyone does.
Dividing the electorate further isn't the solution for any leader. Inciting them to illegal or violent behavior isn't the solution either, unless you aim to dismantle a democratic republic.
I've always felt "us-vs-them", and I believe everyone has, because my peer group has ideals different from others. So we find other groups that share them, and we try harder to be heard, or to exert the influence that the framework of our republic grants to us (i.e. voting) or that society grants to us (i.e. boycotting).
But I do not believe the election itself has caused a divide, it's the candidates (yes, one more than any other, but all have contributed) whose rhetoric has amplified a divide that was there all along.