R.I.P. Scout26
If it is even possible to assimilate all of our legal immigrants it will take a generation or two.
Even that would only be possible if they wanted to be assimilated. In past generations, most immigrants wanted to become Americans. Many of today's immigrants have no desire whatsoever to become Americans. They're just here for the free *expletive deleted*it -- they don't think of themselves as Americans at all.
It's not even "no desire", which more implies, "I'm not going to the trouble." It's actively making it known that they won't join the melting pot and that America and Americans are bad.