According to the Washington Post article A horrifying look into the mind of 9/11’s mastermind, in his own words quoting James E. Mitchell :
But perhaps the most riveting part of the book is what KSM told Mitchell about what inspired al-Qaeda to attack the United States — and the U.S. response he expected. Today, some on both the left and the right argue that al-Qaeda wanted to draw us into a quagmire in Afghanistan — and now the Islamic State wants to do the same in Iraq and Syria. KSM said this is dead wrong. Far from trying to draw us in, KSM said that al-Qaeda expected the United States to respond to 9/11 as we had the 1983 bombing of the Marine barracks in Beirut — when, KSM told Mitchell, the United States “turned tail and ran.” He also said he thought we would treat 9/11 as a law enforcement matter, just as we had the bombings of the U.S. embassies in Kenya and Tanzania and the USS Cole in Yemen — arresting some operatives and firing a few missiles into empty tents, but otherwise leaving him free to plan the next attack.
“Then he looked at me and said, ‘How was I supposed to know that cowboy George Bush would announce he wanted us ‘dead or alive’ and then invade Afghanistan to hunt us down?’” Mitchell writes. “KSM explained that if the United States had treated 9/11 like a law enforcement matter, he would have had time to launch a second wave of attacks.” He was not able to do so because al-Qaeda was stunned “by the ferocity and swiftness of George W. Bush’s response.”
the quote in the actual book is:
KSM said al-Qa'ida was stunned by the destruction caused by their attacks and by the ferocity and swiftness of George Bush's response.