strken parent
Given that most PhD students pay for their earlier education and then do underpaid grunt work as part of their program, the US should already be reaping the benefits. It's only failing to reap them in the sense that more could be gained if they stayed, and that a citizen would be more likely to stay.
Having a fraction of US PhD leave might be a good thing for cross-pollination. The fact that they've left doesn't mean their contacts and relationships vaporize. This could help America stay abreast and integrated with foreign research.