I watched George W Bush the other night and wondered why he didn't do this more often. He's darned good at it. The enemy (press corps) kept throwing him screwballs, and he'd hit them out of the park.
But I did realize that a session like this must be excruciating to him.
The enemy kept asking questions designed to elicit answers along the line "I made a mistake" or "I apologize for my part in 9-11." He handled them extraordinarily well.
I particularly liked his response when asked what mistakes he has made since 9/11. The President looked at the floor for awhile, and then looked up and said "If I think of any, I'll let you know", or words to that effect.
Some people thought he was fumbling; I thought, "There's an old Baja Oklahoma guy who just leveled his opponent."