The difficulty here for President Trump is that this reality punctures a galaxy-wide hole in his gun philosophy - the way to combat bad guys with guns is for good guys to have guns.
So here we are, in the real world, and that fairy-tale scenario did not pan out, making the President's approach to gun control look ludicrous - which of course it is - but he doesn't appreciate the facts pointing that out for the population of Planet Earth to see very clearly.
So, in order to try and reclaim some of the vaporised moral high ground, the President opines that this should have been a 'good guy with a gun', but he fell down on the bravery front.
That makes the loss of life the guard's fault, which it wasn't, and not the government's persistent refusal to address the nation's gun attitudes, which it was.