Ultimately it boils down to the common denominator in all of the comments on this thread - PEOPLE.
People are inherently flawed and are susceptible to those proverbial seven deadly sins, the most egregious being ENVY, SLOTH, GREED, imho.
Historically, every single culture has declined, some into absolute ruin. Whether that decline was precipitated by war or pestilence or just plain neglect, the result has been consistent. We should not ignore history.
As long as PEOPLE are driving the boat, we will always have these flaws and these issues. And the resulting decline.
I would agree with Victor Davis Hanson that the current mal-administration has hastened America's decline far beyond any kind of normal curve. That's SharterJoe's legacy -- destruction of America far faster than even the normal criminals, slothful and greedy bureaucrats, and power-brokers could have imagined.