This whole thing started when he talked about a woman from Somalia, which refused to not support Alcadia. She is now a US citizen. Also in her district, they outlawed the pledge of allegiance. So Trump came out and said if you have a problem with this country, you are more than welcome to leave.
Again Trump does not need to do anything, it is not his job to make his fans not chant something. He only said he enjoyed it, which why not. It's his supporters, his backers the people who were with him since the beginning. Of course, he would side with that they said. It's not like they are saying "This is my country get out, you don't belong here." It's a simple thing if you do not like this country and continue to disrespect it, we don't want you here. Go to some other country and live a happier life. It's like going to McDonald's and finding out you do not like the food. Then for the next ten years making it a daily thing to go there but continuing to bash it every time you go.
Have you heard how Reagan used to talk during his speeches? He was way worse than anything Trump did, but the people loved him. Since so many people can't seem to give Trump a chance, he can't be bold? As a president, it is your job/duty to be bold, not some spectator who lets other countries step on us. That's why a lot of people moved from being Liberal to Trump's side. He speaks the truth, even though it is hard to hear.