From the media coverage into the reasons why this happen, so far I see that the NRA, Trump and the Republicans and the AR-15s are to blame for the 17 deaths.
But from the investigations into WHAT REALLY HAPPENED, it appears that instead, the FBI, local Coward County Sheriff's department were the real failures in this crime. And the program Obama and Holder put into place to reduce crime reporting in the schools, led to a political fiasco of grade A proportions.
This was not a failure of the gun laws or even the guns themselves. This was an enormous failure of law enforcement authorities at all levels from the FBI down to that imbecile Coward County Sheriff and to his deputies on the scene, to carry-out their duties to keep the community and it's citizens safe.
The weapon in the hands of Cruz was the democRAT party and its liberal social manipulation policies.
You nailed it.
Every cause you called out was was instigated or carried out by liberals, leftists and progressives.