I disagree with the idea that professional troops in at least this democracy ( such as it is ) would have allegiance in a progression such as described. When troops talk about fighting for the guy beside them , that is almost a defensive - only sentiment and could never be capitalized upon in the way intimated . And as far as allegiance to commanders goes , this isn't Rome.
Yes , a Puller or a Patton might have in theory garnered that much of an allegiance , but it only goes so far. Pattons troops might have dug in to the Russians under other circumstances , and Puller's people would have gone into hell wearing gasoline underwear with him, but that era of Marines composed the enforcement arm of high preists of the American civic religion. I bet Marcus remembers the day when a WWII Marine from the Pacific theater wasn't just some old guy with history , but a middle aged guy around whom you minded your language and spoke of the nation in only reverent tones. Burning a flag around a vet from Iwo Jima only became a safe thing to do after they reached the age of sixty. I just can't see the killingest SOB I've ever known , Grady Tyner , a man that was at it from Bloody Ridge in Guadalcanal to the Chosin , ever doing something like that, ever.
As for modern troops , believe it or not , that religion persists. I forget who said here recently that current American military are extremely professional and oddly highly ethical considering appearances in reports about soldier misconduct. That is true. I don't know how you could maneuver them to a position of coup , as their understanding of the place of the military is if anything much stronger than it would have been in Grady's time.
This end of it doesn't bother me. Isolated individuals and small groups that have either lost their faith and are angry or are fundamentalists that believe the government may need to be taken back are feasible. Much anything beyond that, no. Anything of the sort , and I really do agree with Tinker on this , would quickly find itself with a Gyrene enema. There is a reason why the Corps is the only military unit that keeps full time , combat ready units specifically tasked to presidential protection ( the whole of Eighth and Eye in DC) , extending out to Camp David. There is a reason Marines run HMX-1. I don't see it.