Sean Hannity ignores it.
Terrorism is a strategy used by a militarily weak group against a militarily strong one, to create fear, dread, and uncertainty among the general population toward some political or ideological end, such as ending military actions by the strong group against the weak. It's not clear to me that Major Hasan's attack at Fort Hood meets the criteria of a terrorist attack, or even a religiously motivated one, though that's somewhat more plausible. His action did share the element of being an attack by the weak against the strong, but he also appears to have had mental issues and an ongoing battle with the military over his desire to get out and not be sent to Afghanistan. There were clear warning signs that were missed or ignored, but it doesn't appear that he was part of a broader plot.
The Fort Hood shootings were a tragedy, and possibly one that could have been avoided. But it certainly isn't an event that provides justification for torture, warrantless wiretapping, the revocation of habeas corpus, and the expansion of "homeland security" to the detriment of our civil liberties. Perino and Hannity want to argue that the Obama administration has made us less safe on the basis of this incident, which makes about as much sense as blaming the Bush administration for the Virginia Tech shootings.
UPDATE (November 27, 2009): As a couple people have correctly noted, I should also have mentioned the post-9/11 anthrax attacks as another terrorist act Perino forgot about. Richard Reid, the shoe bomber, was another.
UPDATE: Hume's Ghost notes that Perino has said via Twitter that she meant "since 9/11," and correctly points out how absurd it is to discount 9/11 for Bush (as well as these other subsequent events she's ignored), while blaming Obama for Hasan's shooting: "...while there were warning signs about Hasan's fitness for duty that could have been noticed by those around him, this is hardly something that would have been on the President's radar. No one was briefing President Obama that Major Hasan was determined to strike a military base; however, President Bush was briefed that Bin Laden was determined to strike in the United States prior to the 9/11 attacks."