> decade of low oil prices (affecting exports), high defense spending (increasing deficit), societal unrest due to the resurgence of nationalism, and slowing productivity

Good thing the US hasn't .. oh.

(the oil price is actually OK as is the trade balance, so far, but social cohesion is fraying and people are always complaining about productivity)

Sure, you can tell now when looking back. But at the time, it tremendously surprised everyone, both inside and outside.

The country could have continued like this for years, if not decades, were it not for a few men and coincidental events.

US productivity is going into things like un-avoidable advertisements from your new Jeep when you come to a stop, embedding dark patterns for everything, and spending all R&D on a tool to replace all human workers. A nation can totally be held together heathily under today's 'productivity'.

Many of these things have been happening in the US for the better part of a decade (or longer).

Did the USSR have an entire administration rapidly and deliberately tearing down their government, or was it more of the cracks in the foundation finally giving out?

Just because the former took a decade doesn't mean that this will require the same amount of time.