Yes, if we remove our migrant population then we literally lose the majority of our food production workers. I think it'll also impact our construction work force, much of our factory workforce, our waitstaff, and various other jobs US citizens turn their noses up at - because those jobs literally would not sustain them and would destroy their bodies over time. Most of these jobs are sustained entirely by the desperation of immigrants trying to escape their prior circumstances.

Edit- added more detail in bold to make it clearer the the issue lies in how these jobs are conducted rather than being with US citizens.