I heard a radio interview today with the man who made the film short in Sweden that Trump saw. He said what he did because of what he had seen in the film.
The filmmaker explained that when he was in Sweden trying to make his movie, he was physically attacked by Mohammedans when he entered certain neighborhoods. While some reports say the Mohammedan enclaves are "ghettos" he explains that most of them are not poor at all but rather are somewhat affluent -- the thing that is most common between them is that the people living there enjoy most generous community benefits. (Europe already has good benefits for communities but these pockets of Mohammedans have even more than elsewhere.) They have managed to enforce keeping OUT any outsiders, that is, non-Mohammedans (aka non-Muslims), which they refer to as "infidels."
He said that he was surrounded by 5 young muscular men who attacked him and beat him up, telling him to get OUT and NOT COME BACK. There is no police protection for him or other media personnel trying to go in and make docuмentaries. The inhabitants don't want to be recorded and they don't want their story to get out.
Nevertheless, this filmmaker managed to sneak in and make his movie, in which he exposes their operation for what it is, and which when he viewed it, made Trump have the reaction he did. Gangs of Mohammedans go out at night terrorizing other neighborhoods, raping women and stealing property, and they're doing it in such a way that they don't get caught. Trump is upset that this could be going on in Sweden, because it represents a threat to America as well, since if they can do it there, they could do it here, too.
They could be training in Sweden so they can come to America and share their training with others.