From an editorial in the Dallas Morning News:

Let’s stipulate that no amount of security can guarantee an end to shootings like the one Wednesday at Fort Hood. A motivated attacker, especially one able to get inside the perimeter, will inflict damage.
This knowledge does little for our sorrow today. This second such horrific event in five years at the nation’s largest Army base leaves us struggling to comprehend and united in grief and anger with those who serve and their families. Four more dead. An additional 16 or more wounded. Too many questions, not enough answers.
And while it’s logical to connect the Nidal Hasan and Ivan Lopez shootings, if only by victims and location, take care to not miss the larger point.
Regardless of what the Army says, Hasan was a terrorist who attacked fellow U.S. troops from a warlike impulse: to protect fellow Muslims on the battlefield. His Nov. 5, 2009, rampage left 13 dead and more than 30 wounded. … Today, he sits on death row.
What we know about Lopez now is that he was mentally ill and, after four months as a military truck driver in Iraq in 2011, was seeking treatment at Fort Hood, living in nearby Killeen with his wife. He dressed for his rampage Wednesday in green camo and shot himself in the head when confronted by military police.
… [T]he military must study and resolve how its internal culture has been altered by 13 years of active war footing, since the initial assault on Afghanistan. According to a Department of Defense survey, about 7 in 10 active-duty military enlisted personnel are 31 or younger, along with about 4 in 10 officers. These young men and women have spent much of their careers — and all of their adult lives — at war.
The stress exacts a toll. How much? Can the military do a better job of screening for mental illness, from recruitment to discharge? And, importantly, can the military use those assessments in a way that’s fair to the assessed and those who serve around them?
Mental illness rarely manifests in mass killing, but mass killing often results from mental illness. We must find a way to study and treat the vast scope of mental conditions without sending the message that we believe everyone with mental illness is a potential mass murderer.