Horizontal inequality, identity politics and the evolution of political dimensions

Progressive thinkers have small differences concerning the realtionship between identity politics and the potential multidimensionality of politics. Scholars like Roemer have been well aware that dimensions such as religion and ethnicity can be manipulated by the rich to make the poor vote for them. Krugman believes that sometimes a focus on horizontal inequality is a lesser evil: "Horizontal inequality is the term of art for inequality measured, not between individuals, but between racially or culturally defined groups. (Of course, race itself is mainly a cultural construct rather than a fact of nature — Americans of Italian or even Irish extraction weren’t always considered white.) And it struck me that horizontal thinking is what you need to understand what went down in both parties’ nominating seasons: It’s what led to Donald Trump, and also why Hillary Clinton beat back Bernie Sanders. And like it or not, horizontal inequality, racial inequality above all, will define the general election.You can argue that it shouldn’t be that way. One way to think about the Sanders campaign is that it was based on the premise that if only progressives were to make a clear enough case about the evils of inequality among individuals, they could win over the whole working class, regardless of race. In one interview Mr. Sanders declared that if the media was doing its job, Republicans would be a fringe party receiving only 5 or 10 percent of the vote.But that’s a pipe dream. Defining oneself at least in part by membership in a group is part of human nature. Even if you try to step away from such definitions, other people won’t." 
In his article, Krugman gives the example of the US as a place where the salience of dimensions evolve because of the intended efforts of politicians, but also for demographic or evolutionary reasons (political scientist Riker argues in "Liberalism versus Populism" that there is a natural evolution of political issues, and he gives the example of slavery in XIX century US). Milanovic in has last book has as one of his final ten questions about what will be important for income inequality in the immediate future this question: "why it is wrong to focus exclusively on horizontal inequality?", and he has a previous less known piece on the determinants of ethnicity becoming salient in politics as opposed to income. The late historian Tony Judt has an article summarizing his views on the bad influence of identity politics for socialdemocracy and ends up saying: "Being “Danish” or “Italian,” “American” or “European” won’t just be an identity; it will be a rebuff and a reproof to those whom it excludes. The state, far from disappearing, may be about to come into its own: the privileges of citizenship, the protections of card-holding residency rights, will be wielded as political trumps. Intolerant demagogues in established democracies will demand “tests”—of knowledge, of language, of attitude—to determine whether desperate newcomers are deserving of British or Dutch or French “identity.” They are already doing so. In this brave new century we shall miss the tolerant, the marginals: the edge people. My people."