One addition and one disagreement:
You mentioned differences between the electorates for Brexit and the upcoming American election, but another big difference is that Brexit was a referendum. A single issue, yes or no. Issue referendums are especially vulnerable to demagoguery, and sometimes turn into referendums on leaders.
By contrast, the American presidential election is about many things at once. Winning requires building a large coalition, and voters who may disagree with Clinton on one thing (e.g. foreign interventions) may vote for her because they prefer her position to Trump’s in other areas (taxes, stop-and-frisk, whatever)
My disagreement is with your claim that Trump is a new phenomenon:
- He’s been the most prominent proponent of the birther conspiracy theory since at least 2011, which helps explain why racists flocked to his candidacy.
- The anti-establishment theme of his campaign was a prominent aspect of the Tea Party, which began influencing US politics in 2010.
- Immigration hawks are a big part of the Republican base, and they’ve asserted themselves in Republican primaries for years. The most prominent scalp they claimed was House majority leader Eric Cantor in 2014, which killed immigration reform efforts. They also may have ruined Marco Rubio’s presidential candidacy, since he sponsored comprehensive reform legislation.
Trump isn’t that new, and Trumpism is older still. Trumpists just haven’t had a champion at this level before.
And, since it’s not new, it’s not going away, even if Trump loses badly.