Neither did Trump say 'all Mexicans'.In fact he said ... "and some, I assume, are good people.". The media twisted it into 'all Mexicans', just like they said that Sarah 'saw Russia from her house' ...
On this, and fighting democRATs boldly, unapologetically, on their own terms ... Go Donald!
So...he doesn't know for sure if any are good people? Because that's what assuming really is, a guess. An educated guess perhaps, but still something you are not prepared to say for sure. So Trum is guessing that maybe a few are good people. And that makes it all better?