I don't think even Tom Clancy could come up with a plot to make this scenario work.
I dunno. I think you have to stretch pretty hard here and there. The whole point is that if he had a few general officers he could do it. You're saying that's impossible, and I'm pretty much with you, regardless of how he treated Mattis and Kelly etc. But the whole point was that that was all that was standing in the way over a short period of time.
So let's go with the worst case scenario and say that for some ungodly reason, the Commander of XVIII Corps decides to back His Orangeness. Maybe the JCS have already resigned. Maybe USNORTHCOM was bypassed. I have no idea. It doesn't really matter.
Commander XVIII Corps is going to know who he can get to make this happen on Bragg. First seize control of the class V and class VII depots. Then follow through with everything else. All he needs is a single Brigade Commander with him at this point. The Brigade Commander only has to make the pitch to his officers after he already has a security team that he probably already knows and trusts. Anybody who decides to not follow the "legal orders of the commander in chief during a crisis" will be quietly placed under house arrest. This is probably going to cover you all the way down to company level. He doesn't need everybody. He only needs maybe 1/3 of the officers and NCOs and 1/2 of the enlisted. Impossible? Maybe when it comes to the officers. I don't think it would be hard to get 1/2 of the Snuffys.
After you seize control of the base you break out your message to the rest of commanders, but you don't even really need to go into a bunch of details. You can just tell everybody else that they have orders to stand to and stay put. You don't have to go into detail on what you are doing.
The best part of having a light unit is that you can easily load them onto FMTVs with tac gear and roll out to DC. You don't need as much logistical tail. You can pick up fuel at Shell. Then you got a 6 hour drive to DC. If General Ripper can take control of the base overnight and have the first BCT at 50% strength rolling towards DC by morning, troops can be in DC by noon.
You don't really need everybody to agree to it. Certainly not the company grade officers and every single snuffy. You just need enough of the NCOs to sign up at that level. 82nd Airborne troops may not have IFVs, but they have enough LMGs to outgun the Capitol Police. The Capitol Police know this and are not going to put up a huge fight. They're not supposed to be doing that sort of thing.
So there is your very worst case scenario, and all it took was a single three star to side with Hiz Orangeness. How realistic? I don't know. That would be the basic plan. I guess it also depends on getting 50% of your NCOs and troops to follow, but they're pretty well conditioned to follow orders. Trump starts relieving other commanders or they resign after refusing to obey illegal orders and you're kinda screwed.
So there's my premise. It all hangs on those people. The whole enchilada. I suppose it always has but it's something you don't think about often.
Could it actually happen? I dunno. Seems like fantasy.