Probably never. The US government has a lot of laws, ignores a lot of things. The issue is more that it is impossible to have an open border combined with any

Probably never. The US government has a lot of laws, ignores a lot of things. The issue is more that it is impossible to have an open border combined with any sort of welfare state. And there is a question about political compatibility - at some point there is a difference between individual migration and an invasion. But realistically, the US had the debate on this decades ago and has decided that insofar as there is a national culture it doesn't consider it threatened by migrants with foreign views. It is a bit late to get worried about it now for obvious reasons.