If Trump wins 2020 then Pence will have the upper hand, if Trump loses its all fair game, and we could see a whole lot of new candidates making their mark. I have been waiting for this for a while, and as a disgruntled Republican who is eager for new faces, let the early speculation commence.
Its going to be a tough road for a Populist unless a Democrat wins in 2020 and its very very close. In 2024, they could still point to an initial election and a narrow loss and say "Trump was just garbage but if garbage can do that well on a populist platform, how far do you think a normal president could get on populism?"
If Trump loses by a lot, it will be seen as an indictment of populism. If Trump wins, that puts a traditional Evangelical-Properity Gospel type in the driver's seat in 2024. If this is the case, maybe Pence will perfect a new form of intersectionalism that blends a lot of Reagan's original ideas with both W's and Trump's.