I'm starting this thread in response to a comment from Thorn in the space elevator thread, that seemed to me a little...stormy? cloudy? Apologies, English isn't my first language and even less Highly Weird English.
I'd say we have already seen some cracks in the Empire, even if not specifically the security flaws that allowed the bombers to attack the space elevator. We don't need to know what's in the Prime Radiant to estimate why the Empire is in trouble.
The imperial statisticians have said that the Empire is expanding, and see that as a good sign. The Emperor seems very keen on peace and stability and the whole genetic dynasty is all about that, so it's safe to assume that the Empire has been steadily expanding for some time. And its resource, communications, monetary and power structures must be geared towards expansion.
But there are signs that the expansion has reached its natural limits. For a start, the Emperor himself seems to be worried that Hari Seldon is right. Another indication is that the space elevator, after being destroyed, didn't get rebuilt. I think the most likely reason is that there is no longer enough space traffic to justify rebuilding it. Other possible reasons would be resource or governance problems in Trantor, that would be an even worse sign of decline.
I could go on, but I'll leave it there.
I have the impression that there are two rather different notions floating around about what is psychohistory:
The bottom-up version, focused primarily on things like resources and secondarily on how people distribute those resources and organize themselves, leaving questions like politics and psychology to the end.
The top-down version, focused primarily around human psychology and language, then looking at social factors and economics, and leaving questions like natural resources to the end.
I've always been interested in the first version, but it seems to me that most people in this forum have the second version in mind.