A short time ago, as such things are measured, Osama bin Laden said this:

America is a great power possessed of tremendous military might and a wide-ranging economy, but all this is built on an unstable foundation which can be targeted with special attention to obvious weak spots.  If America is hit in one hundredth of those weak spots, God willing, it will stumble, wither away, and relinquish world leadership.

A bit earlier than that, Abraham Lincoln said this:

At what point then is the approach of danger to be expected?  I answer, if it ever reach us, it must spring up amongst us.  It cannot come from abroad.  If destruction be our lot, we must ourselves be its author and finisher.  As a nation of freemen, we must live through all time, or die by suicide.

And now we have Barack Obama and Hillary Clinton.