It not "low IQ" it's lack of education, which does lower tested IQ, especially for stuff like crystalized intelligence.
But just in general, throw a random maga into a year of college and their measured IQ will jump a significant amount. It's not they're becoming more intelligent.
Like, think if Usain Bolt didn't start training for running till he was 30. He'd never get to the point he is today, but he'd see massive gains at first due to his genetic advantages towards running.
Similarly MAGA would show giant gains, because they haven't been exercising their brains in ways that an IQ test measure.
Especially with critical thinking, the prefrontal lobe can grow well into your 60s, especially if it's already below average.
But if we're talking about brain differences and political leanings, you really need to be talking about amygdala differences at the same time.