They work, they pay taxes. Culturally, they're "American." In a sane world, one that was pre-Trump, both parties wanted to fix it. Make it harder for illegal immigrants to live here, so more kids aren't brought here while young, and make these people legal permanent residents. That solution would not hurt anyone, and it would be good for the economy. But Trump's base doesn't want an actual solution: they want to punish the browns and see a wall. Not all Trump voters feel that way, but no Trump voter will be persuaded not to vote for him over it.