[HDThoreaun]

You can if you force every immigrant to be educated. Germany's problem is that their immigrants are not. There are more than enough educated people that want to immigrate to America, start with allowing every international college graduate to stay and your most of the way to solving the demographic problem.

Even still, the US is much less homogenous than germany. A variety of cultures is not a problem.

[badpun]

Imagine if 80 million people immigrated to the US over the next decade or two, most of them from non-Christian cultures. I imagine this would lead to, at least, a major political crisis in US history - i.e. major rise of xenophobic far right, talks of secession or even civil war etc. AND, that is in a country that's very open to immigration, compared to Germany.