The Bureau of Labor Statistics indicates about 1 million people in automotive manufacturing (including parts manufacturing) and 2 more million in sales (including auto parts sales, 1.5 million excluding sales) that's a lot of people concentrated in rust belt swing states who would see job instability by foreign vehicles entering the market at race-to-the-bottom prices and quality.

https://www.bls.gov/iag/tgs/iagauto.htm#iag31cesnsaemp.f.p

If you expand the scope to all manufacturing jobs (because auto manufacturing doesn't exist in a vacuum and actions taken to affect the auto industry will also have some effect to most if not all manufacturing industries) that grows to about 13 million jobs

On an unrelated note, they also indicate about 200,000 unfilled job openings in manufacturing every month indicating the industry has a desire to grow but lacks the humanpower to do so.

https://www.bls.gov/iag/tgs/iag31-33.htm