That's quite a tall claim to be making about a country built on immigration. The greatest periods of economic growth in the US are correlated with immigration

That's quite a tall claim to be making about a country built on immigration. The greatest periods of economic growth in the US are correlated with immigration rates. I don't know what "proof" you have but remember that the economic impacts of demographic shifts are pretty broad, so I would suggest you validate that your source is taking that into account, and isn't intentionally biased for political reasons. The overwhelmingly predominant economic opinion is that immigration is very valuable in growing a country's wealth.