What needs to be fixed in terms of intelligence for a successful prevention of terrorism?

Answers:
This is a great question (a rarity in these parts)!
Right now, US intelligence agencies need a better understanding of Middle Eastern culture, and operatives capable of infiltrating terrorist groups like Al Qaeda. This would be SOOOO useful it could effectively end the war on terror by pulling the rug out from underneath them. When the terrorists won't be able to trust that their brethren are US spies, they will tear themselves apart.

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I'm afraid that there is no sure-fire way of preventing terrorism. No matter how many people you make peaceful out there, there's always going to be one who will still want to cause a ruckus and screw it up for the rest of us.
As far as intelligence, there needs to be better communication between the agencies in charge and the citizens. We the people see more and hear more than what the government would like to give us credit for.

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One thing that could be fixed is to stop firing Arabic speaking translators just because they are gay. Another would be for the current administration to reassign his wiretappers to listen to actual terrorist suspects instead of political opponents.