"Where Mr. Trump broke new ground was in a tweet in which he said gun controls would not have prevented the London attacks, because the killers used knives and a vehicle. What kind of American leader exploits a foreign tragedy on behalf of the National Rifle Association? The NRA used to have to do its own marketing in the wake of bloodshed. Not any more."
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One might note that but for England's very tight and effective gun control, the three attackers might have had Bushmasters and multiple clips, as in America.  If anything, the lesson here is that gun control probably saved dozens of lives.  That would not be much consolation to the families of the dead and injured, though.