If he assumes full power without institutional restraint, America could truly transform into a Fourth Reich: a great, ultra-nationalist, exclusive, and authoritarian power in the 21st century.
This rhetoric appeals to a conservative white voter base that feels threatened by globalization and the multicultural demographics of the US.
I don't think it is possible in the US because the two bold parts are in contradiction.
US is not a "natural" country, it is a colony and the ~350 million population are not Americans, they are immigrants who call themselves American. This is why they usually identify as Something-American like Irish-American, African-American, and so on. Something that is not true in a real country like Germany. Which is why "nationalism" has a different meaning too and could lead to "Reich" in Germany but not in the US.
I believe that after centuries and a war that liberated themselves from the rule of the English, they should be considered THE people of that land, no?
It's the same with Australian and that continent.
Of course they have tried to artificially create the concept of "nationalism" in this colony by doing things like mass advertisement of benefits of "genetic/racial mixing" to strip the colonizers/immigrants of their ancestral identity and replace it with a new artificial one but their success rate is still small (30% IIRC) and the result is indifferent people who are more like potatoes rather than nationalists!
The main thing that used to unite all these completely different people under the same flag was the promise of "land of opportunity" something that was always a lie and is now long dead which is clear from Trump's main campaign ad/fake promise that won him the election: M.A.G.A.!
I don't know what sort of "nationalism" debate you're trying to start, but a country with people who actually fought and help liberate countries in Europe from the rule of the "Third Reich" should have some sort of "national identity" inside them.
Back to the topic of Trump and the pressing rate cut, and because the Federal Reserve is usually late in cutting rates, do believe that Trump is right to keep forcing Powell to cut the rates as soon as possible?