Well, nothing changed. It's not the Democrats doing. It's industry bring in Mexicans for cheap labor. For example, in chicken processing factories. Americans don't want these jobs. But corporations don't want small town Americans to blame them for the foreign influx, so they blame Democrats in a constant drum beat on right wing media. "Democrats need new voters. They get them by bringing them here and putting them on welfare." When their people are in charge, they get them to claim they're building a wall and they're dealing with this influx that happened under Democrats.
Corporations and industry shift the blame away from themselves for any social problem caused by the influx of cheap labor, even though they are responsible for it. Nothing changes under either party in power, only the blame rhetoric gets changed. That's political science in America.