Speculations that "this is the work of a jihidi" infiltrator are at this point vacant fear-mongering. They make reference to possibilities that are without clear, modern domestic U.S. military precedent.
The last comparable incident of which we are aware was at Fort Bragg in 1995, when Sgt. William J. Kreutzer Jr. opened fire on members of the 82nd Airborne Division's 325th Airborne Infantry Regiment during their morning exercise on post. Both of the partners in this service were on the ground, writing about that incident at the time. The motivations in that case were personal, not political and Kreutzer was mentally ill.
American Muslims mourn the deaths and fear backlash because the identified gunman - Maj. Nidal Malik Hasan, a 39-year-old from Virginia - is a muslim who was apparently stressed to the breaking point by his scheduled deployment to Afghanistan. The Council on American-Islamic Relations responded:
No political or religious ideology could ever justify or excuse such wanton and indiscriminate violence. The attack was particularly heinous in that it targeted the all-volunteer Army that protects our nation. American Muslims stand with our fellow citizens in offering both prayers for the victims and sincere condolences to the families of those killed or injured.
It is to the credit of U.S. Sen. John Cornyn, R-Texas, that he urges moderation in response to events at Fort Hood.
Wajahat Ali writes in the British Guardian:
After an American soldier's tragic outburst of violence at Fort Hood, Texas – the army's largest US post, with some 40,000 troops – dominates the headlines, a fear-mongering hysteria concerning his supposed religious motivations is taking priority over questions regarding his mental health.
The FBI had already been prompted by his online postings to investigate him.
Gen. Robert Springer got it right in comments to WRAL when he said it was "another example [like Kreutzer] of someone that went, we use the term, ‘Off his rocker,’ at the moment and attacked his own troops.”
The Army encourages soldiers to seek help, and the base commander at Fort Hood explicitly did so [.pdf] a short time ago. It is a searing tragedy that Nidal, a psychiatrist and "mortified by having to deploy" to Afghanistan, was apparently somehow unable to do so before exploding.