“In the future, if Republicans do not do better among Hispanic voters, we are not going to be talking about how to get back Florida, we're going to be talking about how not to lose Texas.”
Romney's hardline approach to immigration during the primaries has been covered exhaustively, but I'll just add this -- it was very much like the win-now-lose-later tact that former California Gov. Pete Wilson rode to a reelection win in California in 1994.
That was the year of Prop 187, and some far-sighted Republicans predicted his aggressive pursuit of the issue would cost the GOP for generations, and look at how blue that state has turned with spill-over effects across the country.
That's not to say Hispanics wouldn't be hugely Democratic without it (As this poll shows, Hispanics just generally prefer far more government involvement than whites, for example), but it seems to have been the catalyst for it.