Assassination. As far as I know no one tried it on President Obama and no one has tried it on the current occupant. But maybe some have and no one knows about it.
Successful assassinations have been few. "They" tried it with President Reagan who, by comparison to the current occupent was a tiny pimple versus a face full of pus. I dunno. Maybe the current occupant owns the hearts and souls and trigger fingers of all those who are weaponized and waiting to hear his dog whistle. We wait and watch and wonder. Not all of us of course. Just most of us.