this is my question, how does he dispute that alcohol or drugs wouldn't make a difference when he admitted that he was drinking too much when he was at the age he would be serving in the guard)
from the interview with Dr. Phil
Bush, now 58, gave up alcohol at 40 after concluding he was drinking too much. He often refers to the power of faith in that process and once referred to his youthful drinking as a "young and irresponsible" stage of his life.
Fear of Flying
A new source has emerged with what she says is personal knowledge about why George W. Bush prematurely left his Texas National Guard unit in 1972--because nerves, fear and a possible drinking problem were affecting his ability to pilot his F-102A plane. If true, this information further confirms a growing body of evidence that Bush has not been candid about his departure from his unit. At various times the President and his spokespersons have offered shifting rationales, from the planned eventual mothballing of the F-102As, to his doctor's unavailability to give him a flight physical, to a professional opportunity in another state.
However, Janet Linke of Jacksonville, Florida, says that it all came down to an inability to perform. Linke is the widow of Jan Peter Linke, who was brought into Bush's National Guard unit to replace him when Bush left the unit and the state for Alabama in May 1972.
http://www.thenation.com/doc.mhtml?i=20041011&s=baker