The campaign slogan “America first,” it turns out, is already taken. But Santorum is proposing a serious response to the GOP’s national electoral challenge. Republicans, in this view, need to shift their focus away from high earners to struggling ­middle- and working-class families; and they also need to choose between courting the working class and courting Hispanic voters, because immigrants take jobs and depress wages at the low end. The party of the worker, therefore, must be the party of immigration restrictionism.

Santorum is often thoughtful; in this case, he is thoughtfully wrong. His economic case is overblown. Economists sift and dispute the evidence. But the long-term impact of immigration on native wages seems to be slight — slightly positive for those with a high school and some college education, slightly negative for those who don’t graduate from high school. These effects, however, are overwhelmed by other economic trends, such as the advance of technology and globalized labor markets. The white working class does have many problems, but competition from low-skilled immigrants is not among the biggest ones.

Effectively focusing on the white working class also buys into the notion that Republicans can win the presidency by running up the white vote. This might, for all I know, work in the next presidential election. If (a significant “if”) Hillary Clinton is the Democratic nominee and gets 80 percent of the minority vote, Republicans would probably need (in an estimate by National Journal’s Ron Brownstein) about 63 percent of white voters. (The highest percentage Republicans have ever gotten was Ronald Reagan’s 64 percent in 1984.)