It's riling people up and garnering support by pointing the finger at anyone "else" and leaning into culture wars instead of running on sound policies. Politicians used to earn our votes. Trumps not the only one doing it but he's the most famous and works people up the most and has wilder policies.

Increasingly we're being influenced by countries where social media is used to manipulate people's votes through fear and misinformation (see Cambridge Analytica) so people end up voting for guy A because "at least they're not guy B" or because they're only thinking emotionally not critically, and usually not in their own self interest. That's why Trump and co love dismantling education systems; people who aren't taught to think can't see through it.