Who's Watching the Watch List?

Heading for Oakland from Seattle to see my grandkids last week, the Alaska Airlines check-in machine refused to give me a boarding pass. Directed to the ticket counter, I gave the agent my driver's license and watched her punch keys at her computer.
Frowning, she told me that my name was on the national terrorist No Fly Watch List and that I had to be specially cleared to board a plane. Any plane. Then she disappeared with my license for 10 minutes, returning with a boarding pass and a written notice from the Transportation Security Administration (TSA) confirming that my name was on a list of persons "who posed, or were suspected of posing, a threat to civil aviation or national security."
No one could tell me more than that. The computer was certain.