Keyword: TEMPORARY!!!
Many work visas start out temporary and evolve all the way to Green Cards. It still takes an American job.
I'm sure the U.S. workers who were displaced by these cheap foreign workers are consoled by the fact that the cheap foreign workers were here temporarily.
Iirc he also hired some Italian stone masons to repair historic building as they were not available here. Then he hired Americans to work along with them to learn the trade
And they were here legally.
H-1Bs are supposed to be temporary too.