Yes, you're right, they do seem to play this up. That's strong evidence against the conspiratorial explanation I mentioned.
people's votes tend to shift "rightward" when they are afraid for their lives
Yes, I think this is true. But I seem to remember (but cannot cite) that people also "rally around the flag" and support the leader more--even if the leader is not "right."
Moreover, the present government still has some additional political incentive to play up the risk of terrorism, especially if the administration can blame it on the previous one. "Al-Qaeda is really scary--man, our predecessors sure did let their guard down."
Yesterday I was using the Global Terrorism Database to check some suprisingly low figures on what percentage of terrorist acts are committed by Muslims. (Short answer: Worldwide since 2000, about 80%, rather than 0.4 - 6% as given in various sources.) But I found some odd patterns in the data for the United States. Look at this chart of terrorist acts in the US which meet GTD criteria I-III and are listed as "unambiguous":