The Reagan Revolution, which basically crystallized modern conservatism in its current form, was based on the "fusion" of three strands of the conservative movement: social conservatism, free markets, and a hawkish foreign policy.

Sure. Is something appropriate at one point in time supposed to be frozen in amber and *always* kept that way? If that's the standard, what would JFK say about today's democrats? Think FDR would be down with letting criminals have more rights than victims?

Pendulums always swing about a center axis.

Right-wing populism rejects those premises. They very much reject letting private markets determine where the jobs go, where international labor and capital flow, or even the idea of a global free trade system at all. They want the government to intervene against private actors (like, say, a completely private university) rather than leave it up to the markets - they very much want government to be an active and powerful participant in deciding contested issues among private actors. That's an express rejection of the fusionist conservatism that Goldwater, Buckley and the National Review espoused back in the day - where issues of virtue are left to private actors, not the remit of the state.

They don't "reject" letting private markets determine where things go, so I don't think that's correct: what is asked for instead is a fighting chance that's aligned with the national interest.

Is it in the United States' best interest to buy critical products and medicines from China? Or to allow China to willfully evade restrictions under NAFTA and dump cheap components into Mexico? Or to continue to play the game of allowing them to steal American IP at will?

As for isolationism, that's more nuanced. Asking NATO countries to spend what they're required to spend as outlined in the charter is hardly inflammatory (and in fact Gert Wilders' new government in the Netherlands is formalizing doing exactly that).

I'm not sure what your example of 'intervene against private actors' refers to.

The only major departure from conservative ideology is that of fiscal restraint. Trump was horrible on the score, and that's a pre-COVID statement.