I think it’s not clear that the causation flowed that way. I think it’s at least partially true that the Republican base was much more isolationist and protectionist than its “establishment” elite, so any significant candidate that played into that was going to get some level of support.

That, combined with Donald Trump’s massive pre-existing celebrity, talent for showmanship, and utter shamelessness got him across the line.

I think it’s fair to say that at least partially, Trump didn’t shift the base - rather he revealed that the base wasn’t where the establishment thought it was.

I don't think that aligns with the reality of the opinion formation. There was a strong subset of isolationist and protectionist views before 2015.

I know that by "dear leader" you mean to imply that Trump did something unfair/wrong/sinister/etc ("just like Hitler", amirite fellas?)., but a leader of a large group of people, by definition, is good at persuasion.

Franklin Roosevelt moved the Democratic Party in a direction very different from its first century. The party's two previous presidential nominees were a Wall Street corporate lawyer (John W. Davis) and Al Smith who, despite also being a New York City resident and state governor, so opposed FDR by the end of his first term that he founded an influential anti-New Deal organization. During the Roosevelt years the Democrats lost significant support from traditional backers, but more than made up for it with gains elsewhere in what became the New Deal coalition.

Similarly, under Trump the GOP lost support in wealthy suburbs but gained support elsewhere, such as Rust Belt states, Latinos (including places like South Florida and the Texas border region), blacks, and (according to current polls) young voters. We'll see whether one compensates for the other.