As an example, America would never have been first on the moon if it were not for a certain German engineer Wernher von Braun.
> The international collaborations that it thrives on are largely formed via exchange of students.
1) Students are on F visas, so they are unaffected by H1B changes.
2) There is no magical reason that students educated in another country in this day and age have a markedly different tradition of thinking about fundamental science. The internet has largely erased the differences in access to the latest research in top institutions around the world so the only thing that remains needed for high quality research is a pool of bright people. Perhaps there are some educational tradition differences between Europe and the US but US postdocs are largely educated in the US itself so those differences aren't really affecting current US research anyway.
3) Given the current labor and supply demand in academia, this pool of bright people can be satisfied by either US researchers or foreign researchers, and since there is ample choice between the two, the research of great import still gets done by just as many smart people as before, so once again, I fail to see the "problem" for great research being done.