3) Trump vetoes the NDAA but doesn't invade Seattle
I think this is the most likely option, because he has two reasons to veto it: so that he can invade cities, and also so he can support the racist slave-owning traitors to our country known as the Confederacy. (At least the slave owners in the Union weren't traitors...which is a pretty low bar to clear)
4) Trump vetoes the NDAA and also invades Seattle
Like you said,
troops don't get a pay raise and are ordered to fire on peaceful protestors and looters alike. If Trump's polls took a hit for a photo op, I can only imagine what would happen following a domestic use of
lethal force on unarmed civilians. Because if this happens, things will escalate and troops will fire actual metal bullets this time.
It would no longer be possible to claim "Trump's not a dictator" and the world, already backing away slowly, would turn its back and run. I honestly think we'd see sanctions placed against us -- legally.
And I worry about the violence when federal troops
uninvited assault a US city. A US city that has its own police, its own National Guard...and most importantly, sympathetic neighbors.