Yes, the problem IS the GOPe, and you put your finger on it when you mentioned “30 years of massive immigration has finally closed the door on that advantage.”
GOPe was a driver behind that mass immigration. Still is. Why do you think Trump couldn’t get the wall funded by Paul’s Ryan’s GOP-controlled House, let alone taken up by Mitch’s GOP-controlled Senate? The Koch Bros and other Big GOP Donors want open borders, and that’s what the GOP has been delivering for decades.
No no no the lacking of funding for the wall and for border security is entirely on Trump he’s the leader of the entire party if he had wanted total funding he could have gotten it very easily.
After Mexico told him to take a hike he kicked the can down the road to where we are today which is no wall and a tiny improvement on border security