The logic is  - the stupider the US Government - riven by internal dissension, driven by narrow special interests etc. - the more other powers - and even the EU will gain by comparison - especially if they are effectively led in terms of their own national interest - as Russia, China, India etc. seem to be now.

My major concern with that scenario is that:

1. The US could behave even more irrationally in decline, and start an even worse Iraq type war with Iran or Russia -0 or possibly even a World War.

2.  In the absence of very strong global governance and enforceable international law provisions (which the neo-cons have also done their best to destroy) such an emergent "multi-polar" political system will be as dangerous and unstable as that which existed prior to WW1.

3.  I like most American's, even if many seem politically naive, and hate to see them and their country dragged through the mud.