Even domestic flights...
Every single PNR on a US domestic flight is also sent to the Department of Homeland Security, as the airline cannot print a boarding pass for you until DHS approves it. Prior to 9/11, various agencies would send watch lists to the airlines who then had to put it into their systems, but now it is all centralized.
Frequent Flyer data is jealously guarded by the major carriers, they often won't even share it with other departments at their own airline. They make way too much money flogging credit cards and selling miles, and won't share their database.
My background - I worked in travel IT, primarily airlines, for the last 35+ years.
A.