America was a nation of settlers, not immigrants. There are differences. It was the settlers who built the American nation and gave it its flavor that the later immigrants came to be assimilated into. This shouldn't be a hugely important point, but the way immigration enthusiasts go on and on about a "nation of immigrants" the point needs to be raised.
Now, those people - let's name them, Mexicans - may "work hard", but they are also league leaders in highschool drop out rates, English language difficulties and whole host of other social pathologies. All these things need to be considered, not just their hard work.
Immigrant families don't grow old? Who will pay their social security? Yet more immigrants? This isn't a solution; it's the postponement of a solution. (And if you're a conservative, why do you even care about social security?)
But flood your country with millions of Mexicans (or better yet, Algerians or other Muslims), most of whom are just here out of greed, who grudingly speak your language, let alone wish to assimilate into anything, and boy, you can sure write your own foreign policy then, right? Not.
Anyway, America isn't dying (neither is France), it's just reproducing at a lower rate.
Yet, for all that, they still vote overwhelmingly democrat.
In many ways:
They left the 'old country' on the understanding they were never going back, and had little choice but to leave the old ways behind and assimilate into something new. Mexicans live a stone's throw away and are greeted with multicultural policies that ask them to stay as Mexican as they can. Then, if that wasn't enough, they demand Americans learn Spanish, rather than they learn English and replace July 4th with Cinco de Mayo. On top of that, many of them don't even belive they're in a new country: afterall, "we didn't cross the border, the border crossed us"; the southwest is, properly, Mexican territory.
And, since you asked, the 'great wave' immigrants were all white. That's not supposed to mean anything, but fifty years (or whatever) later, you couldn't tell one of them from someone whose family had been in America since the 17th century. Racial (and cultural) similarity also mean more intermarriage, which obviously greatly accelerates assimilation. Today's immigrants are almost entirely non-white, so that effect cannot be relied upon.
And of course, the 'great wave' eventually ended. Not naturally, but with a moratorium on immigration. That also helped immensely in assimilating all those immigrants. In contrast, there seems little prospect of the current wave of immigration ever ending (not talking about only Mexico, now).
None of this should worry me, as I don't think I'll ever live in America again. But it does worry me, because if America doesn't check its immigration, Australian immigration enthusiasts will use that as an excuse to do the same thing to Australia. Fortunately, Australians tend to be a whole lot saner about immigration, but there's still the risk.