> We've had multiple presidents assassinated but still had continuity of power.

Sure, with the peaceful transfer being recently violated for the first, but probably not the last time. The literacy rate in the US continues to decline, and the US keep losing respect on the world stage which is only going to get much worse over the next 4 years.

> Some of us who are optimistic believe that the uniqueness of the U.S. lies in its favorable environment for innovation (e.g. YC),

The US doesn't have an especially favorable environment for innovation than other first world countries, arguably it has less given the lack of regulation.