Of course they do! When you bring in low-skilled workers who are willing to work for LESS, obviously the current LEGAL low-skilled workers will suffer.
That's why Trump wants a vetting system in place to bring in HIGHLY-SKILLED workers who WANT to be AMERICANS.
What happens when you add HIGHLY SKILLED workers to a business? The business functions more effectively and efficiently. They make more money, they can pay their workers more money, the owners and shareholders get more money.
Everyone wins. So of course the dems are violently against it. Because American success is bad for the democratic party.