The politics of hate, of bigotry, of fear. As long as it works electorally, it will continue. Politicians don't succeed by elevating things like decency and ethics above "winning is the only thing." Says a lot about the electorate, sadly.
Large-electorate elections have always been susceptible to misinformation, to disinformation, because in large-electorate elections, it's not possible for the voters, as a whole, to really be personally informed. This becomes more of a problem as the opportunities to generate and spread disinformation have grown - and grown exponentially in the internet age. Modern social media are different than traditional media in many ways - and one of the most problematic, IMHO, is that they're completely un-curated. It's left to the individual to figure out what's factual, what's fantasy, what's deliberate falsehood...and recent experience suggests that individuals simply aren't very good at that. Most people do not, or cannot, invest the time to effectively sort through the noise and the deliberate lies.
I'm not at all sure that the experiment initiated in 1776 and 1789 can survive; a system based on smallish electoral districts and a voting population that was reasonably informed may simply not be able to function at much larger scale, in an era where disinformation has been commoditized and commercialized for profit.
I'll be 66 this month. More and more, I'm kinda grateful that I'm not 30 years younger - because it's going to be a rocky ride.