Well, actually it is just racism.
Half the undocumented people didn't illegally cross the Southern Border, they came here on work, student or tourist visas and overstayed their welcome. But you guys are only crapping yourselves over the brown people coming in over that border.
You could solve the undocumented immigrant problem easily.
1) Establish a National ID program, with biometrics, so that only people authorized to work here can get jobs.
2) Go after the people who are openly breaking the rules by hiring them.
Problem solved. But this has never been about solving the actual problem. It's been about pandering to the racism of awful white people. The same awful white people who will drive down to the Home Depot and hire a bunch of day laborers to finish that job that looked a lot easier on TV.