Republicans have reached their 1984. I don’t mean this in the Orwellian sense, though Republicans have more than their share of Orwellian impulses. Rather, I mean that the kind of divisions that have characterized Democratic presidential primaries since the 1984 contest between Walter Mondale and Gary Hart have now popped up in GOP primaries as well: This year, Republicans are dividing along lines of class.

According to data compiled by the Wall Street Journal, in all the states that have voted thus far, Mitt Romney has won 46 percent of the counties with incomes higher than the statewide median, and just 15 percent of those with incomes beneath the statewide median. Rick Santorum, by contrast, has won 39 percent of the counties with higher income, and 46 percent of those with lower income.

These numbers — a product of the kind of residential-sorting-by-class that Charles Murray documents in his new book, “Coming Apart” — reinforce exit polling that shows Romney’s strongest supporters come from households making more than $100,000 a year. Indeed, the higher up the income scale, the higher the level of Romney support.

These numbers look familiar to anyone who has tracked Democratic presidential primary voting for the past three decades. Beginning with the Hart-Mondale donnybrook, Democratic voters have often clustered by class. In that year, Mondale, the presumptive favorite, was given a tough race by Hart, whose supporters were disproportionately upscale, younger professionals more concerned with environmentalism and cultural issues than with the bread-and-butter staples of New Deal politics. Mondale’s key backers were more downscale voters, disproportionately union members and African Americans, and his platform emphasized more traditional liberal priorities.

Their contest was the first in which the changing class composition of the Democratic Party affected internal politics. Professionals, academics and scientists were beginning their decades-long journey from Republican to Democratic ranks, bringing with them a host of concerns that were new to the party of Franklin Roosevelt and John Kennedy. And from 1984 on, Democratic primary voting has characteristically divided along class lines — Michael Dukakis’s upscales against Richard Gephardt’s downs in 1988; Bill Clinton’s semi-populists against Paul Tsongas’s professionals in 1992; Al Gore’s union backers against Bill Bradley’s neo-gentry in 2000. In 2008, Hillary Clinton was the darling of white working-class voters while Barack Obama soared among white professionals.

The platforms of these Democratic candidates spoke to their distinct constituencies — Gephardt campaigned against free trade, Tsongas championed cuts to social welfare. But just as important, if not more so, were the class signifiers that the candidates, deliberately and not, displayed. Some were more comfortable in blue-collar settings, others on the wine-and-cheese circuit, and voters had no trouble discerning the candidates’ cultural and socioeconomic comfort levels.

Until this year, Republicans hadn’t gone very far down this road. They tended to anoint the establishment front-runner — two Bushes, Bob Dole, John McCain. Far-right outsiders such as Pat Robertson, Pat Buchanan and Mike Huckabee drew disproportionately from a more downscale constituency, but none of them got very far. The Bushes, Dole and McCain claimed significant support across the Republicans’ income spectrum.

This year, two things are different. First, Romney is not claiming that kind of cross-class support. He personifies Wall Street at a time when even Republicans don’t like Wall Street. Second, the downscale wing of the Republican Party, more inclined toward reactionary cultural appeals than are more upscale Republicans, has grown. Just as upper-middle-class professionals have become more Democratic, so the white working class has become more Republican.

As the race narrows into a two-candidate contest between Romney and Santorum, these class-based divisions are likely to grow. It’s not that there are great policy differences between the two. Romney may be hurt in Michigan because he adamantly opposed the auto bailout, but Santorum opposed it vociferously as well. Nonetheless, in Michigan and Ohio, Santorum will campaign as the GOP version of the working-class hero — a candidate with blue-collar roots who wants to eliminate taxes on domestic manufacturers.

Neither Santorum nor Romney will champion policies that could really help the white working class — the unionization of service-sector workers, say, or federal subsidies for strategic industries — but Santorum clearly feels its pain and summons the ghosts of religious and patriarchal orders that once regulated much of working-class life. Romney comes off as the guy who closed the plant, after which those orders collapsed in a heap.

Welcome to the Democrats’ world, Republicans. Welcome to your own class war.