The GOP is already irrelevant. They can’t win a national election anymore.
GHW Bush 60% of white vote = 400 EV
Romney 60% of white vote = 200 EV
Immigration reform will not make the GOP any more or less relevant.
That's a little misleading. The GOP took huge hits because white turnout was lower than black turnout by almost 10%, and non-white turnout was pretty good. Ultimately, Romney was viewed by what would have been (white) Reagan Democrats as an elitist who would screw the little guy. In both 2008 and 2012, white turnout was tepid compared to 2004. Ultimately, Obama's whole schtick is getting minorities to the voting booth.