The radical Left has apparently run out of brainwashable citizen-subjects, are not succeeding in indoctrinating the rest of us into their six decade old cultural revolution, so they need fresh minds and bodies to refill the social program ranks. Seems the Left discards cultures they've exploited out of useable political resources before moving on to the next.
The average American citizen is useless to them as currency, so what do they do: throw open the gates. A new, highly exploitable population comes flooding in. No problem. They're undocumented, poor, 'refugees', so the younger American generation--always out to save the world--embraces them and votes for US Reps who champion new programs to completely fund the lives of the horde of new Americans.