It has a lot to do with him. He doesn't actually have an opinion on any policy issue. For various political reasons, Trump decided to let RFK dictate public health policy according to his extremely delusional ideas. Yes, there was an antivax movement in this country for many years, just as there has been misogyny, racism, and transphobia. Trump has normalized and supercharged all of these moronic and dangerous ideas.

I have not been following measles in Canada, so I can't address that.