One of the problems with election campaigns is that ideas get presented to the general public as wild, unprecedented and beyond the pale - and the general public has no idea if that's actually true, or if these same kinds of ideas are quietly implemented all the time behind the scenes.
When Donald Trump talks about a temporary halt on immigration by Muslims, or by people from certain countries with known ties to terrorism, the news media acts as if no one has ever imagined such an idea before. And Trump is treated as a wild-eyed lunatic for suggesting it.