That's such bs. It's a typical Republican talking point: "If you're against people owning guns, you give up your guns first and see what happens". It's not an original or particularly good argument, but you're really straining credulity by suggesting this has anything to do with assassination of his rival.

It was a rhetorical question defending the idea that all Americans, including Hillary, should be able to arm themselves in self-defense. Watch the full source material. "Watch them do X and let's see what happens" is a common form of framing a rhetorical question in New York when complaining about a bad idea. Sure, his mentioning of a specific individual in the context of gun control hypotheticals (instead of using a hypothetical individual) is an insensitive gaffe, but that's really all you can reasonably conclude about the statement.

There are activists who routinely call for mass disarmament of citizens (entirely seriously and not as a form of rhetorical exploration), and it is unreasonable to conclude that the activists are "hinting" at or condone any kind of authoritarianism or genocide that may coincidentally result after such a policy is implemented. Don't muddle the discourse further with similarly unreasonable conclusions.