I had a thought: in previous decades it was advantageous for the US to invite academics from China because we could impress them with our highly developed standards of living. We could work them over with intelligence and maybe even turn them as US assets and informants. As life in China gets better and life in the US gets worse, though, this has become a hindrance as those same academics now see the squalor of US cities and decline of US prestige. Now we need to keep them out or the whole charade of US supremacy will collapse. Now they can only be allowed to view the US from movies and television.