We are, indeed, a nation comprised overwhelmingly of the descendants of waves of immigrant ancestors.
However, that was a different time, before America had expanded coast to coast, and when it still desperately needed settlers and cheap labor to build our railroads, cities, etc.
But all of that was completed many decades ago, and that same demand no longer exists; instead, we are perfectly capable of fulfilling such needs internally.
We also no longer have free land to give away to anyone willing to settle it, as we did in the late 1700s and throughout most of the 1800s.
America is not yet "Full-Up" and ready to hang a "No Vacancy" sign on the Statue of Liberty, but we're much closer to that state of affairs now, then even 30 or 40 or 50 years ago.
And, of course, there is no need to keep taking-in New Folk until we, ourselves, are standing 10-high on top of each others' shoulders, as the overcrowding in so many 3rd-world shit-holes makes those other places seem to us who are accustomed to a far less crowded land.
I like my country less-crowded, and see no need to continue packing 'em in until we look like a metaphorical can of sardines.
We can certainly continue to provide for a modest influx of New Folk, strictly enforcing a Quota System of some kind, but we just don't need the numbers, like we used to.
And, the sooner we admit that to ourselves, and the sooner that we stop beating our breasts about being the World's Refuge, the sooner we'll begin to get a grip once again on Immigration.
Obumble's latest Shamnesty attempt certainly isn't the answer.