If GWB did not "keep us safe" then what was all that about: 5000 US combat deaths, hundreds of thousands of Iraqi and Afghani deaths, the torture, the wiretapping, the trillions of dollars spent, even the long lines at the airport?
All of which bothered people at the time; they violated norms of behavior that most had come to expect about our country. Norms like: The USA does not go to war except in defense. The USA does not invade countries at will. The USA does not torture people. The USA is not big brother. The USA is not so fiscally irresponsible as to pretend that making war doesn't cost money.
Many people already knew that such beliefs were illusions. But for many, they were still thought to be true. They were norms, or boundaries, people thought were in place.
The Bush administration violated all those norms and justified it in the name of the nation's safety. "He's keeping us safe" became the binding myth.
What's a binding myth? An explanation:
People should not punch other people. That's a norm of behavior most people adhere to. If I tell you that you should go up and punch another person, you would say that you won't. After all, it's a norm that people do not just punch other people. But suppose I persuade you that that person needs to be punched because he insulted your mother's honor, and you then do it. I have bound you to me because I am able to make you do what you know you shouldn't. And I have bound you to me with the binding myth that I uphold your mother's honor.
Once bound, I can make you punch whomever I want by invoking the myth of your mother's honor. But what if you learn that I am not protecting your mother? The moment you realize that I am not about your mother's honor at all, you also realize that you have been punching people for no good reason. To avoid that self-knowledge, you will go to any length to preserve the myth that your mother's honor is both sacred and also under constant attack.
"Keeping us safe requires the abandonment of democratic and constitutional norms" is the myth by which the Bush administration bound the nation to it in the days after 9/11. To preserve the power of that binding myth, more dangers must be found, and more norms must be necessarily violated.
That binding myth is so essential to self-justifications of the Republican party at this point that to even remember that George W. Bush had been in office for nine months on September 11th is to say that unthinkable. We can see the anxiety such truth provokes, that people immediately think Trump is blaming Bush for 9/11.