Why didn't jets intercept the airliners since they had numerous warnings of terrorist attacks on 9/11?

1. Training exercises on 9/11 were used to paralyze the military, by making personnel at NORAD's Northeast Air Defense Sector confused over whether the terrorist attacks were real or just simulated. These training exercises included a scenario in which a plane crashes into a building, on the very day it actually happened.

2. They were ordered not to.