Last time I was in the rustbelt part of Pennsylvania, I had a guy tell me that Allentown is full of Puerto Ricans these days, and he added "I bet 90% of them are illegal immigrants."
He is correct that there has been a population surge among Puerto Ricans in Allentown. He is of course incorrect in his estimate that 90% of them are illegal immigrants, since everyone from Puerto Rico is a naturally born US citizen. When I informed him of this, he refused to believe it. When I pulled it up for him on my phone to show him, he insisted it was either wrong or "a brand new rule" that illustrates the need for Trump's heavy-handed immigration approach, because there's no way we should just be letting them in like this.
The point is that this guy griped about illegal immigration, but when he found out the people he was complaining about were here legally and not actually even immigrants, he was even more pissed.
That's just one guy, but he's surely not alone. It accounts for much of the energy behind this nativism, which is being fueled by racism.