There's an experience of getting really into the lore. I go through periods when I listen to a ton of Warhammer 40,000 audiobooks, and the ton that comes before whichever novel I'm currently adding to the pile does bring a certain kind of pleasure that isn't present if it were instead a novel set in an entirely new universe. Each book hooks onto worldbuilding that I'm already familiar with, and thus each character or story beat gains a depth and richness that wouldn't have been there before. Comic fans get the same thing. I imagine soap opera fans do, as well.
It is a genuine pleasure, too. That doesn't mean stories with heavily developed and studied lore are always better than stand alone. But lore emersion can be pretty great, and its pretty-great-ness is intelligable.
The thing is, though, lore emersion come with a less pleasurable flip side: irritation with storytelling decisions that clash with what you imagine the lore to be. Continuity errors. Comic book characters with changing powers. Reboots that abandon everything you've spent so long learning. It can provoke a fan response of anger, fighting over which lore or which continuity is the correct and accurate one. These fan responses can turn vicious, and not just when they're motivated by racism and misogyny, though many are.
And that's, in part, the deal with MAGA. The racism and misogyny, yes, but also the love of lore and the anger when something introduces an incogruency.
For most Americans—and particularly for the culturally reactionary ones who form Trump's MAGA base—American history isn't really history. It's not a series of actual events to be studied objectively and probed thoughtfully. It is instead American lore. Like learning everything there is to know about Star Wars or about Warhammer 40,000 or about the endless variety of heroes who make up the Avengers, American lore is a comprehensive story any new event can fit into. And that you, if you're American, can fit yourself into, too.
So when those people who approach their country's past the way a convention attendee approaches the United Federation of Planets gets told things about their history that clash with their lore, or when people insist on interpretations that don't line up with their sense of it, they have this polarized and angry response.
It's more violent and destructive than Star Wars fandom, because they see the stakes as higher and they have the state at their disposal. And the cultural resentment, racial animosity, and fear of shifting gender roles and power that infects many fandoms infects this one, too, but with that violence of the state giving it greater force. It's worse, in other words. But it's still analogous.
Lots of Americans want their lore, and they want to fight over their lore. The MAGA project can be viewed as just another fandom, committed to its canon and its cosplay. And they think their lore is getting corrupted by people who don't understand it or who hate it or who want to reboot it into something different. They're wrong. Their lore is largely pretend, a simulacrum of American history—one meant to center people who look like them and talk like them and have the same beliefs as them, and decenter everyone else. They enjoy feeling like the worldbuilding they've done is coherent, and they hate the incoherence introduced by critical examination or diverse perspectives. It's not about veracity. It's about comfort with the familiar, no matter how much damage is does to the actual country, with actual people, their lore is built and parasitic upon.
Unfortunately, seeing MAGA as fandom doesn't provide a fix. No one's figured out a fix for toxic genre fandom, either.