Much as Rome was backed by its legions...until it debased its currency to the point that its economy faceplanted and it could no longer pay its legions

If this is true, get ready to get drafted because Russia just refused to accept anything but Rubles. Without the requirement of trading oil in usd, no one will buy it as it is inevitably going to inflate away. Without foreign countries to buy our dollars, those dollars stay here and further inflate. This is a negative feedback loop ending in a mathematically certain collapse. Buckle up, we're heading for the mother of all crashes.

All that military might is payed in USD. The US military holds its reserve status and relies on its reserve status for its survival. Its a tenuous existence that could end very rapidly.