Sure, but the argument in this thread suggests that the US is making an overall loss by funding the research carried out by foreign nationals. This is hardly the case - the value of the research is worth more than the manpower costs spent on them. Is there greater value to be had by encouraging them to stay within the country? For sure.

Look at postdocs - the US gets them at a pittance, they are more productive than PhD students and rather mentor them; and unlike graduate students, are usually overwhelmingly foreign nationals.