You don't need Nate Silver to figure this one out. If you are as old as I am (b. 1944) it's very simple and it goes like this.
When I was a kid there were White, Blacks and a few Hispanics - very few actually. The Asians all lived in the two Chinatowns in New York and San Francisco or above their little laundries in other cities. Pakistanis and all the other Pacific people didn't exist, ditto the Latins. Plus, the Blacks didn't or couldn't vote and there weren't anough anyone else's to make a difference.
So all the Republocans had to do was put a dent in the Southern vote, which had been Democartic since Reconsttruction, and they could win. Which they did.
It really doesn't matter now what position the Republicans take on any issue. It doesn't matter whether they find a Hispanic like Rubio or a Pacific-rimmer like Jindal. The Democrats are the non-White party and, thanks to Obama, they all vote.
Einstwin was once asked to explain how he figured out the universe and he said, "Keep it simple and make it simpler." The Democrats are on the verge of making it simpler. Let's hope they don't try to complicate it.