Yeah, the National Union Party is a little bit forced, though I've tried to chock it up to intense fear of more terrorist attacks. Regarding Prince being allowed to stay in power, my thought was that PMCs have so permeated the US intelligence agencies and military that they know everything that's happening in the country, and the civil war to remove them would be very, very bloody because of that.Well, that sucks for just about everyone. Makes OTL politics look totally calm and sane, really. My biggest doubts about realism concern the idea that the Democrats would go for a national unity ticket just because they can't win (I don't see that happening: national unity typically occurs only when the nation faces existential peril) and the notion that Prince's coup could just succeed without ending in a messy civil war. No way the generals are happy taking orders from a damned mercenary, so the Republicans who had intended to use him as a puppet only need to get some hadline military leaders on their side, and they've got a counter-coup that Prince really can't beat. Result: military junta controls the US, de facto or de jure. (The insane foreign policy can still end up the same way, even!)
Anyway, despite those minor points, it's certainly a very interesting scenario. One wonders how long this kind of imperialism can last. It's bound to be unsustainable in the long term. If we look at the fiscal realities of the USA in OTL, this ATL will see the USA collapse before long. Either the costs of the imperialist policies become unsustainable and the USA has to withdraw (likely following up militaritic imperialism with despotic isolationism), or the imperialism is maintained by cutting all other expenditures and raising taxes incredibly, thus turning the USA into a autocratic command economy army-with-a-country(-and-no-social-security-at-all-in-spite-of-really-high-taxes). Which spells messy revolution.
And after the US occupation ends, I can see the Islamic world turning into ISIS writ large. Very large.
I'm glad we're not living in this ATL!
My thinking is that the Prince regime is eventually overthrown, which would cause mass US withdrawal, and yeah, a massive power vortex.
Regarding the nature of the Prince regime, it's much more traditionally Republican, so in favor of free trade and government programs than the OTL 2017 party.