That seems like it's been Buchanan's thing for far longer than just his most recent comments. Probably he'll die on this particular hill, whether or not it has any basis in reality.
That said, while I think Buchanan's racial politics are deplorable and confusing (surely the measure of a free society is not the color or ethnic background of its people, but its ethics and the value it places on the freedoms it has cultivated? To put it another way: am I danger because my grandmother came to this country in the 1930s from Mexico, ~50 years before I was born? And if I am not, then why would the children of immigrants today necessarily be? Because they're not white like Pat Buchannan? What does whiteness have to do with values?), I also think it's fairly easy to see a glaring difference between immigration to the United States and to Europe, even though it's not particularly 'PC' to talk about
that, either: In the United States, we are surrounded by majority Christian countries to our south and a majority "guys named Doug" country to our north, and so the majority of our immigrants tend to share at least something of a common base in that sense. On the other hand, most of the immigration into Europe as of late has been from former colonies with majority Islamic cultures, such as North Africans in France, Pakistanis and Iraqis in Britain, and of course the ill-considered 'guest worker' program in Germany which has led to a considerable Turkish minority in that country over the last few decades.
So I don't think you can easily simply transpose one situation onto another and say that because XYZ may be going on in Europe, then that is comparable to what is happening in the USA or could happen in the USA. Even if we had open borders (which we don't, despite the Republican talking point on this issue), most of the people who come here do not have quite the conceptual and mental leap to make in coming from, say, northern Mexico to Texas, Arizona, New Mexico, or California as the average Somali would have in going to Sweden, or the average Afghan to Germany, or whatever.
But even that has nothing to do with skin color or ethnicity, necessarily. I've known several Afghans and Somalis in my life, and they were kind, appreciative of their adopted homeland, and very pragmatic (if I had to guess, being forced to flee your home country at a young age to escape Islamic extremism
can have that effect on people). Mixed in with those people, though, are those of the same backgrounds who would go on to threaten to bomb the Mall of America and secretly go back to Somalia to fight with Al Shabaab and other similar craziness. So ideally, in terms of positions to be taken on immigration/borders/etc., there should be somewhere between being a racist jerk and being a '100% open borders for everyone; caring about who you let into your country is racist'-type liberal do-gooder at other peoples' expense, and most people should be able to occupy that middle ground without having to sacrifice either their hearts or their brains.
Pat Buchanan, unfortunately, is not most people.