The leaders of great powers usually find it convenient to have one (or rarely two) great enemies. Ideally the enemies should be powerful enough to focus the attention of the people, but weak enough that the great power is unlikely to actually be destroyed at the hands of this enemy. This situation allows one to unify the nation with relatively low risk.
Clearly that is what the Republicans wish to make of the terrorists. They are the enemy in the dark that the USA can rally against indefinitely. Actually creating more terrorists is good for the current regime - eventually those new terrorists will do something spectacular enough to cement their role as "viable enemy" even further. Without those occasional reminders people might forget about them, and they wouldn't serve their purpose.
Cheers,
Ben