Notice his phrasing (after lamenting about 'another mass shooting')..
"..they know the dangers of serving abroad, but today they faced the unimaginable violence that they wouldn't have expected here at home"Well yes, had they no knowledge of what happened at Fort Hood. or LITTLE ROCK. Sort of like this CNN anchorette. There was certainly precedence, regardless of how both events have been spun.
Also, in saying we would 'do everything we can to try to prevent them', ie, mass shootings or whatever this turns out to be, he seems to be hinting that something can be done to stop crazed jihadies or lunatics bent on murder-suicide or just plain mass murder. Ironically he used the same language after Benghazi over a year ago--how we were going to investigate to prevent such events from ever happening again--and nobody is currently in custody. But it's pretty clear what he means.