I personally see the American global position (whether you call it the benign or reluctant hegemon or simply the uni-polar moment), as a unique entity in an extraordinary historical context and thus beyond comparison with any European predecessor (much less, ancient).
One of those unique traits is that America is at once the world's unrivaled super-power and world's greatest debtor.
It seems strange that it was Ferguson himself who pointed out this anomoly back in 2004- which may reinforce his notion of a declining power but doesn't really support his comparison with other historical examples.
Then again, I still largely agree with Jeff- this is a crass overeaction to a global recession.
What people forget is that they are seeing countries like China, Russia and India become great powers once again- not super-powers. Their structural vulnerabilities are, in many ways, far worse than America's.
The last 20 years have been a period of flux and American hyper-power was always going to be transient. The world is probably returning to its more natural state.
Worth remembering that America still has more billionaires than the next 10 countries put together and half of the world's total. Still, America needs to cut its debt for sure (but I'm British so we can hardly talk).