We could have a billion Americans and keep employing them productively. Immigration has been America’s superpower for 150 years. The real problem is monopoly firms that suppress wages of workers and innovation at the same time. The same monopolies that outsourced our manufacturing. All of which started with deregulation and tightening of immigration controls.
Yes, the simplistic "immigrants are competion" narratives always disregard the fact that immigrants also contribute to the economy and uplift it. For instance, there is a credible theory that the "immigration crisis" was instrumental in managing the inflation crisis: https://fortune.com/2024/04/12/immigration-inflation-economy...
20 million? You think the US population had an additional 20 million population growth? And that we just absorbed that? That’s probably breaking a record or two.