Which countries would benefit most from an American brain drain?

That's a good start, but it's not the whole story. There will be a lot of talent returning to China, India, and South Korea, etc., for lack of options. Recent graduates that is. Will be difficult for those countries to take full advantage of these talents, but they might pull it off.

Yes. Immigration is hard. You need to learn a new language, adapt to the local culture and city design, navigate the increasingly hostile immigration system, and distance yourself from your family.

In the past, dreams of American opportunity made the tradeoff worth it. But now we're Magaland when the president sometimes crashes the economy on purpose and immigration officials randomly detain scientists at the airport. It's hard to believe that top engineers and aspiring scientists will continue to give it all up for a shot at life here