American here, and I am an academic historian. It is a personality cult. History will show you (as you well know) that there have been several demagogues in the past who promise to make things ‘great’ again. People get brainwashed. America can be v. insular; many Americans don’t have passports and don’t know about other cultures/ways of life. Globalisation is threatening to them.
The financial crisis, 9/11, COVID, school shootings/gun culture, opiate crisis, inflation making houses unaffordable, all these things have made people fearful. There is also little social safety net in the States and unbridled capitalism has eaten away at the middle class; huge wealth disparities. I’ve stayed in South Pasadena in affluent neighbourhoods, and see homeless camped out on the lawn of the public library/people living in cars. This has been normalised, and people worry that will happen to them. They are scared.
The American dream is starting to crumble, and because the States is a confluence of all sorts of cultures, and fairly secularised, who do people turn to for comfort? A demagogue who promises everything will be OK if they can be in power.