"He has to keep the USA safe from.............what?"

You may want to refresh your memory of the November 2015 Paris attacks, I know 9-11 is now too distant a memory.  I finished Boston in 2013, was changing in The Common and heard the bombs go off.  I don't walk around scared, but kinda glad there is law enforcement to track terrorists down and provide security to make sure others don't do it again at big races I attend.