"This tragedy is all the fault of President George W Bush and the National Rifle Association..."  This gentleman served starting in 2009 and did not serve his tour until 2013, nearly 4 years later.  Obama could have stopped the war in that amount of time as he promised but he didn't.  There's no way you can blame this on President George W Bush.  And to still try and think the two are correlated?  I'm scratching my head to see how you connected those far apart dots.  
Get over it.  Bush cannot be held responsible for events happening nearly 8 years after his departure.  Also, it's ludicrous to blame the NRA.  This man was in the military and knew how to use a gun-HE made that choice.  Why don't you start with placing the blame on the one that pulled the trigger?