Again, from yesterday's Meet the Press:
SEC'Y RUMSFELD: ...I presented the president a list of about 15 things that could go terribly, terribly wrong before the [Iraq] war started.[...]
MR. RUSSERT: Was a robust insurgency on your list that you gave the president?
SEC'Y RUMSFELD: I don't remember whether that was on there, but certainly it was discussed the possibility that you could have dead-enders who would fight.
OK, I guess we have three explanations for Rumsfeld's statement that he can't remember whether he considered the possibility that there would be a post-war insurgency: 1) he's lying, 2) he's senile, 3) he's incompetent. All of those things disqualify him for the job.