You are assuming that the protesters are only reacting against Trump's promises to crack down on illegal immigrants. Some of them might be, but I think they are reacting against a heck of a lot more than some political candidate promising to better enforce existing laws. I can think of all sorts of things Trump has said that might anger Hispanics or (legal) Mexican immigrants.

There are also a lot of people protesting Trump for all the wrong reasons, or in ways that make Trump look like the grown-up in comparison. It's hard not to have at least some sympathy for him in those situations. Still, I try to judge people by their own statements and actions, not the statements and actions of the worst of their detractors.