I heard before Clinton that local LEO's could carry their sercive weapons concealed on commercial aircraft, but a Clinton executive order outlawed this practice. If this is true, I think he is partly to blame for the WTC attacks. If there had been armed LEO's on that flight or, even the threat of armed police, would have changed everything.

The only LEO's that have been able to always carry on the planes are the Feds.  Local cops would only be able to carry as part of their "duties" like prisoner escort of fugitives or if required by thier assignment at the time.  The airlines have always required a letter from the agency head (Chief or Sheriff) detailing the assignment of the reason to carry on the plane. Even after that it was up to the planes Captain to allow it. He could if he wanted to, take the weapon and secure it in the cockpit (usually they wouldn't, but they had the authority to while the plane was in flight).

Other than that it is, or I should say was, easier to declare the gun in luggage.

You heard wrong.  LEO carry post-Clinton was very much the same as pre-Clinton.  IIRC, the only change was that the LEO had to take a short training seminar prior to doing so, and that may have been in effect before Clinton.

Ironically, this training requirement for LEO’s was a very small part of extensive new FAA rules dealing with airport security and terrorism.  

These were originally supposed to go into effect about 1994.  As of the end of 1999, which is when I retired, they had still not been implemented.  

These new rules (assuming they were ever implemented) were obviously a total failure.