A third question

In view of the 9/11 commission’s criticisms of the U.S. government for not being prepared to deal with hijackers using commercial airliners to attack buildings, reader Robert Stakel (via his wife) has a third question:
Assume that the military and the FAA were fully prepared to deal with this eventuality and, at the time the first hijacking was confirmed, the Air Force put F-15s in the air with instructions to shoot down the commercial airliner if it approached a major metropolitan area. Assume that, within an hour, four commercial aircraft were shot down.
How long would it have taken for impeachment proceedings to begin against President Bush?