I'm also aware of the realities of the Russian economy and have no concerns over them or the Chinese driving the dollar from its perch.
Well, with your four econ courses, you should realize that this is not going to happen overnight. But with our reliance on international support for our empire, it is not going to take much to start the ball rolling down the hill.
Our military might is still the greatest in the world and imposing our “will” on countries is key to maintaining the reserve status.
But just as any empire can be toppled by one small group of people “begging to be shot” buy resisting that will—so goes the empire.
You are looking at it as a micro event. Pull out your macro book and see how small, incremental events in one place can impact the larger economy.