US has/had the best schools in the world. US provides/provided remarkable academic independence (tenure, etc). US provides/provided the best expected economic return to foreign scientists.

As we dismantle those components via xenophobia, anti-intellectualism, funding cuts, and so on, trends will change. Already I see a substantial uptick in my PhD/Academic friends moving to Europe as we cede our historic advantages.

If, in say 15 years, China provides better schools, or better economic returns, or (perhaps unlikely) better independence, or all 3, then scientists will go there.