I don't think great man theory has anything to do with this. US is becoming isolationist because the material conditions are declining, and a large chunk of the populace is now seeing the empire as a drain on them. That's what's making the isolationist rhetoric popular. Meanwhile, nationalist governments that get in power in Europe will almost certainly start doing trade with Russia and China again. We are already seeing this with Hungary right now. It's basically the only way to stabilize their economies, and US has absolutely nothing to offer there.

Aside from radlibs, most Europeans don't actually see Russia as their main problem. They might not like Russians, but they're not interested in a war with Russia, and they don't want to make further sacrifices in their standard of living. At the end of the day, it all comes down to material conditions.

I don't buy into the great man theory either, but Trump doesn't exist in a vacuum- I'd call him the manifestation of mass disenfranchisement, disillusionment, and disaffectedness by white, working class America, its petty bourgeoisie, and those true and halfways sensible (ie. not seeking WW3/forever wars) nationalists- in other words, he is the representation of AmeriKKKa's traditional power base, its reactionary, predominantly white settler foundations.

And these groups are indeed angry, and in many ways understandably so (other ways less so). Neoliberalism and the natural progress of capitalist, imperialst society towards a monopolistic, rentier-based economy has done a number even on the imperial cores, and they see the empire no longer truly working for their interests (ill-gotten as said interests often may have been), but slowly eroding their livelihoods instead. They see the imperial plunder declining, but also their share of said plunder declining (and their in-group of white settlers increasingly joining the rest of the world as part of the menu instead).

I'd also have to correct you here- the US military is not exactly the ones running the show- rather, the military-industrial complex, and a host of countless other corporations, in an unholy marriage with the political class and financiers, are running the show. The military is simply the mangy dog of the empire- the tool which they use to terrorize goatherders in oil-rich regions of the world, and also their primary means of cannibalizing the wealth of the empire as-is (that of the imperial cores)- of effectively waging a class war, against the working classes, but even against the petty bourgeoisie, to the benefit of corporate/financier America and the actors in its political theater.

I'd argue, in this environment, there is only one way to "package" a war, particularly a great war, to the western populations- they have to grant them a slice of the imperial spoils, and improved welfare/concessions. Yet this is not on the table- regardless of how the Biden admin or various Eurocrats have hyped it up- the political-financier class has a chokehold on said ill-gotten profits, as well as all levers of power within the west- and by all appearances it seems that they'll fight to the death to keep things that way. What benefit have average Americans, or- worse yet, Europeans, seen from their middle eastern misadventures? Or from the outpouring of billions (of their own taxpayer dollars, or those of their childrens' futures) into the MIC in the name of Ukraine/Israel/Taiwan?

This isn't saying that the west will fall into isolationism- frankly, I think the blob (the financiers/politicians/intelligence agencies/MIC/what-have-you) would sooner kill off Trump or any other politician who would dare actually, feasibly start moving the country in that direction. What we're seeing now, and what I suspect is likely to continue, is that the increasingly hollow shells of empire will move onwards, with their political/financier classes having to whip it forwards every step of the way. Personally I don't think that's a recipe for consolidation- hell, if anything, western society is tearing apart from within, with each crack of the whip, and with each step forward into an ever-worsening neoliberal hell.