You're just flailing about wildly now. But lets get at least one thing straight here.
All of it. It's good that you've recognized political instability as an aspect of weakness, but you're still trying to narrow down abstract concepts to one specific action, event or person. For example, maybe the election of a senile old fart who can barely manage to string a coherent sentence together with help from a teleprompter as president was the trigger that made Putin think now is the time. But it would hardly be the one and only reason in and of itself for Putin to think the U.S., or any other nation for that matter, had become too weak to oppose him.So what on your earlier list do you think is most indicative of political instability?