Nativism will always play well amongst a certain selection of the electorate, and a natural consequence of such a policy is borderline racist rhetoric from the fringes.
True, but the GOP has always had a very nativist element dating back to the former Whigs; they seem louder and more powerful now than ever.
I see what you are saying about the "Loud and Powerful Factor"(which I will get to in the next paragraph) but a significant number of GOP Voters favor immigration reform(just check Pew Research polls) as evidence of this.
Now "The Loudness and Powerfulness Factor" yeah pundits and talk radio hosts like Mark Levin, Ann Coulter, and Laura Ingraham are very vocal against any path to citizenship for the 11 million in the US illegally. I think the Baby Boomer Generation Republicans share those 3 pundits/Talk show Host Views on immigration so that's why that message is so powerful. I saw Ann Coulters book intro of her new book " Adios America" on C-Span yesterday afternoon and she dodged any questions that Ben Shapiro(who was the questioner) asked her about winning new Latino Voters. I was little more than moderately disappointed about Coulter's book intro on C-Span overall. She basically thinks Latinos are just basically Democrats and there is no use off trying to win them. She wants to do "A California Strategy" circa 1994 and get 20% of the Black Vote like Governor Pete Wilson did to win re-election. I just think it's just not possible to do a "California Strategy" circa 1994 in a Presidential Election.
About the nativism factor Italians and Irish used to vote Dem(FDR and Truman) in the 1930's and 1940's I think. I do wonder how much the immigrant vote helped Truman in 1948 win since Thomas Dewey(R) thought he would win that election. Dewey in 1948 sounded like Romney in 2012!