Answering my own question...

Why are we asking this question?

What is America’s biggest national security threat?

Answer: 'Cuz the GOP has managed - again - to frame the narrative.
The U.S. is a weak, threatened nation.
We are vulnerable to attack from all quarters.
We must remain ever-vigilant.

I'm sorry, folks, but in my world, the U.S. is NOT a weak, threatened nation.
We are a vibrant, strong nation... and worrying about the bogey-man is an absurd waste of time and energy.

Let's move forward!