Democrats have been rallying against inequality long before a grumpy socialist ran for president. Barack Obama in 2012 called for a new minimum tax for millionaires and billionaires on his way to defeating an opponent he painted as an out-of-touch plutocrat. Even Bill Clinton ran in 1992 on a plan to tax the top 2 percent of earners to fund tax relief for ordinary Americans (though he ultimately abandoned the proposal to focus on deficit reduction). But Bernie Sanders’s insurgent campaign reflects a party that’s seized on the issue of economic disparity as “the defining challenge of our time,” as Obama himself put it.

Sanders’s determination to run as a single-issue candidate hasn’t been a great political strategy in recent weeks, as the focus of the race has rapidly shifted to terrorism and foreign policy. But in many ways, his campaign has already accomplished its mission: to force inequality to the forefront of the Democratic primary and move the party’s center of gravity leftward on the issue in 2015 and beyond. “The top one-tenth of 1 percent today in America owns almost as much wealth as the bottom 90 percent,” he said in a speech at Liberty University in September. “And in your hearts, you will have to determine the morality of that, and the justice of that.” Just a few weeks later, at the first Democratic debate, Hillary Clinton was forced to defend the very merits of capitalism—but not before decrying the need to curb the excesses behind “the kind of inequities we’re seeing in our economic system.”

This is partly because the push for economic populism has come not just from outsiders, but also from within the Democratic establishment. After the party took a drubbing in the 2014 elections, the Democracy Alliance—a group of wealthy liberal donors—shifted gears to focus on economic inequality, in part by funding more groups aligned with the populist left, as National Journal’s John Judis details. These donors have helped put more institutional muscle behind the focus on inequality, funding left-leaning think-tanks like the Roosevelt Institute and the Center for American Progress, which is closely aligned with the Clinton campaign. Both groups have put out detailed reports that focus on reducing economic disparities through investing in infrastructure, eliminating corporate tax breaks, and raising women’s labor-force participation—all policies that both Sanders and Clinton have embraced in some form.

In an about-face, Republicans have tried to seize on the issue this year as well, though in their own fashion. “The truth of the matter is, big government benefits the wealthy, it benefits the lobbyists, it benefits the giant corporations,” Senator Ted Cruz said during October’s GOP debate. “And the people who are getting hammered are small businesses, it’s single moms, it’s Hispanics. That is who I’m fighting for.” At the same debate, Ben Carson similarly blamed government regulation for hurting ordinary Americans: “Doesn’t hurt rich people if their bar of soap goes up ten cents, but it hurts the poor and the middle class.” Even Romney has gotten in on the act, decrying that “under President Obama, the rich have gotten richer, income inequality has gotten worse.”

Republican ideas, however, haven’t taken the same turn as their rhetoric. The reality is that Carson, Cruz, and Jeb Bush all support tax policies that are the inverse of the Democrats’. They benefit the wealthy far more than ordinary Americans, with the assumption that spectacular growth will take care of the rest.