Well....since one of the definitions of the word "bless" is "to pay homage to, to worship and exalt, to adore and to praise, to give thanks to and to honor"
Bless God America .... adore Him, worship and praise Him, give Him thanks and honor Him.
The sacrifice was and still is great. Since God is all knowing, He still made that sacrifice knowing that a very large majority of those billions He died for, would reject Him. Even to the point of saying it never happened, He doesn't exist and persecuting those who do believe that there was no greater love or sacrifice, than Jesus our Lord on the cross.
Yes, it's very sad that 50 people died. However, just an FYI. You can't legally purchase an assault weapon. Maybe you are uninformed that the AR in front of 15 (AR-15) does not mean Assault Rifle or Automatic Rifle. It mean Armalite Rifle after the company that developed it.