I have read in a couple of places over the last couple of years that people with more fearful personalities tend to be more conservative and, accordingly, to vote for the GOP. People who have more fearless personalities tend to be liberal and to vote for Democrats. Those in the middle are sometimes capable of being frightened enough to tilt them toward GOP candidates.
This is why it sometimes seems that the GOP and al Qaeda are in cahoots. They both want to frighten Americans, so there is a convergence of interests. If al Qaeda did not exist, the GOP would have to invent it. In a sense, the GOP did invent the version of al Qaeda that many of its dupes have bought into, the one where al Qaeda is an existential threat instead of a bunch of yahoos in some caves.