For Mexicans, he said "they're rapists" without limiting the number. He then said some of them are good people, which is confusing and contradictory. Deciding what he really meant is a matter of interpretation and you'll never know if you have the right answer or not. This is, of course, a constant theme with the Trump campaign: say something outrageous, but with just enough wiggle room to explain it away as something else.
As for assassination: "If she gets to pick her judges, nothing you can do, folks. Although the Second Amendment people — maybe there is, I don’t know." This was later explained as a reference to the pro-gun political power, but that makes no sense: Supreme Court justices with lifetime appointments don't care about political activism.
I don't agree with the approach, but do you understand why he said this? The idea was to vet people coming into the country to prevent homegrown terror. It's a real thing, and people are concerned about it. I doubt that it'll work, the problem is more nuanced, but it's not a ridiculous idea.
>said illegal Mexican immigrants are criminals and rapists
No, he said that Mexico sends their worst, not that all Mexican immigrants are criminals.
>and suggested that his supporters should assassinate his opponent
Source?