The output of the US's domestic anti-terrorism effort is low for the resources invested. Most of the FBI's terrorism arrests are wannabes. They get a report of somebody mouthing off in a bar or mosque, crank up a sting operation, get some dummy to go through the motions of trying something, and claim they've stopped a terrorist.
The DoD/CIA operation to find foreign terrorist leaders and kill them seems to have paid off. Anybody identified as a major leader in Al-Queda has a short life expectancy.