Exactly. The US is a leader in technology pretty much exclusively because of immigration. As that reverses, we can expect the US to fall behind, and fall further behind, over time.
60% of all CS researchers in America are not American. 55% of all engineering researchers.
When everyone goes home America loses the majority of it's research output, plus the extra Americans who choose to join them. I suspect a great many Americans will choose to join them, for personal or professional reasons. Why try to get a grant in the US, where the rules change whenever Trump sneezes, vs a stable, consistent system in the rest of the OECD?