It's hard to be selective when considering all of the ways in which American public discourse has gotten worse on account of the 2016 election, but my vote for the worst change is the now-constant recourse to grand conspiracies to explain (across the political spectrum) failures or bad behavior.
Like many people around the world during the Cold War developed an all-encompassing worldview based on the near-omniscience of the CIA (a view that persists to this day in much of the Middle East), people now imagine dark forces on The Internet having almost limitless power. You can't fart in some parts of the world without someone blaming the CIA for it, despite the reality that the CIA couldn't even figure out that some of its own (Ames, Hanssen) were Soviet spies.
Now there is a shadowy Other – sometimes Russia or The Kremlin, sometimes Bots, sometimes merely They – capable of engineering any imaginable outcome and a few that aren't imaginable. Your candidate lost the primaries? Rigged! Rigged by powerful conspirators! You got caught writing some embarrassing shit on your old blog? Hackers! Time-traveling hackers! And most recently, did you get caught plagiarizing (an act that, thanks to easy and ubiquitous tools like TurnItIn, is now almost ludicrously simple to detect)? The people who pointed it out are part of an "oppo campaign"! Well of course.
The fact that a phrase like "oppo campaign" or the extremely popular on social media "Kremlin op" have gone mainstream is a good sign of the extent to which reality and Tom Clancy fantasies have been conflated. A couple years ago this kind of conspiratorial thinking would have resigned any public figure to the lunatic fringe. Now nobody bats an eye. Everything is a conspiracy. Everything is a product of nefarious forces. It's like the upside-down Occam's Razor; never accept the most obvious solution when a mindlessly convoluted one wherein you become a victim will do.
That last part, I think, is key. People who spout this stuff when they are caught red-handed don't even care how plausible their stories sound. It simply is a matter of reframing the story to make themselves victims. Once they construct a victimhood narrative, then supporters innately get defensive and rally. It doesn't have to be true, just plausible. And we are living in an era in which the commonly accepted definition of "plausible" is rapidly expanding.