All Bush had to say was
"If we truly lived in the fascist world you think we do, you'd be led outside and shot in front of everyone for an example."
or
"I'm tapping your phone? Are you talking to AlQaida?"
Either of those would have been great responses, but you didn't really expect Bush to come up with them did you? Now, to be fair, it is hard to think on your feet, especially in front of an audience, so one can cut Bush some slack. But still, it was a bit disappointing that he didn't come up with something better.