Prager is a relentlessly honest thinker. If he has arrived at a conclusion, it is because he can back it up with facts and logic. I doubt he takes anything from Buchanan.
This is a very important piece, and he fleshes out a point that I have also made in the past. People arrive here with a culture. It is rare to impossible for someone to give up everything that that are, or to have the culture of America already, so they will inevitably change to some extent the culture of the area that they move into. It would be less change with smaller numbers of new immigrants. But, we have massive numbers of immigrants right now.