Domestic Spying and Common Sense
The only two ways to prevent terrorist attacks are luck and intelligence. Intelligence means espionage. If it wants to prevent attacks from outside of the USA, the goverment must spy outside the USA. It it wants to prevent attacks from inside the USA the government must spy inside the USA.
Intelligence is largely the interception of enemy communications. Today, communications is largely electronic: Phone, E-mail, etc. Only broad-band interception and selection of communications can possibly to work to catch the terrorists before they act.
Common Sense!