I think the world is getting hardened to Americans shooting each other.
Absolutely nothing will be done about this. Exactly the same as after every other slaughter. In a few days, or weeks, some other nutter will kill a load of kids or Gays or churchgoers and the process will repeat.
Its just part of your nature and collateral damage in the fundamental right to own guns and kill each other.
The last I recall, with very few exceptions, there are approximately 75 to 80 "million" private citizen, legal gun owners in the United States who harm no one and are safe with their firearms. Apparently, being on a terrorist watch list doesn't make it illegal to purchase a firearm. This is clearly the fault of the government, who knew about the Orlando Jihadist and did not try to stop him. Also, potential gun-grabber Clinton stopped the investigation into the mosque the killer attended. Again, the fault of the government.
We legal gun owners represent are no threat to your or anyone else's safety. The real threats are:
Burglars who steal guns (make it a lengthy mandatory prison sentence for stealing firearms).
Straw purchasers (people buying or stealing guns for criminals (again, give out lengthy mandatory prison sentences for those who knowingly sell to criminals).
Gangs (guns obtained illegally and currently are responsible for most gun crimes).
Lone Wolf Jihadists.
Mentally ill.