This was a terrorist act. Ralph Peters gets it right in "Fort Hood's 9/11" in the Washington Post. (I highly recommend reading the entire article.) This was the act of a fanatical Muslim who tried to contact Al Quaeda, who questioned his patients because of their commitment to the War on Terror, who made radical statements to his co-workers, who listed himself as a Palestinian on a Muslim dating site, and who was evidently under investigation by the FBI for months.
Everyone is so scared of being sued for not being politically correct that no one did anything. No one just snaps. There are an abundance of warning signs, and for whatever reason, Army and FBI officials failed to act. Just like Cho at Virginia Tech, or the snot nose punks at Columbine, or any other mass shooting. There are warning signs for anyone with the guts to recognize and report them.
Call this for what it is - Domestic Islamic Terrorism.