Today, I flew from Dallas to Newark with a layover in St. Louis. I was on American for the first leg and United for the last. Although I suffered no particular humiliation during the security checks, I was a bit taken aback by the fact that I had to exit Terminal C in St. Louis and re-enter Terminal A to catch the United flight, and had to pass through security again. According to one of the locals there, pre-9/11 there was a walkway between the terminals, but since then, changing terminals means taking off your shoes and belt and playing the TSA game a second time.
There was a secure passage between terminals A & C long after 9/11. This current inconvenience is temporary and has to do with the restoration of the main terminal building from danage sustained by a tornado that directly hit the building a couple years ago. I have been flying into and out of STL since 1993.