Happen soon?  Already happened and likely to happen more.  Agree that US needs to address and prevent true danger.  Perhaps a good idea would be to "ban", or hunt down and remove, the type(s) of person who share common traits with the following:  Al  Capone (Valentines Day, etc.); Charles Manson (Tate LaBianca); Jim Jones (Guyana); Byran Uyesugi (Xerox shooter); Grace Fortescue (Massie case Murderer); Dylan Klebold and Eric Harris (Columbine); Seung-Hui Cho (Virginia Tech); James Holme (Colorado Theater shooter); Adam Lanza (Sandy Hook); Timothy McVeigh (Oklahoma City bomber); Dylann Roof (NC Church Shooting), etc.