It is the second plane that haunts the mind, curving on a course that seems to descend right out of a waking nightmare. Even before it struck that ugly steel and glass tower, there was already a dreadful familiarity to it. Somehow we’d seen its shape before. The Hindenburg in flames. JFK’s head blooming open on the Zapruder film. The Challenger space shuttle exploding live before our eyes in the stratosphere on an impossibly sunny Florida day. The Waco fire incinerating women and children in those Texas winds. The events of 9/11 played out like a horrifying novelty show, seared into the brainpan of the nation by thousands of instant replays.