Most Democrats want their party to emerge from the impending primaries united in its effort to defeat President Trump in the 2020 presidential election. This is certainly understandable, especially since many of them assume that Trump’s unexpected Electoral College victory in 2016 partly owes to the divisions sowed by the race for the Democratic nomination, when Hillary Clinton’s path to nomination was slowed by the surprising socialist sensation Bernie Sanders. Another bruising primary season, so the wisdom goes, will doom Democratic solidarity, making it easier for Trump to win reelection.

Dreams of unity notwithstanding, it seems likely that the Democratic primaries will be yet another bitter slog.

Dreams of unity notwithstanding, it seems likely that the Democratic primaries will be yet another bitter slog. This is especially true if Sanders chooses to run again, since many of those who opposed his bid for the nomination remain angry about the role he played in 2016. But it’s likely the forthcoming primaries will be nasty even if Sanders decides not to run, and instead hands the socialist mantle off to another candidate.

The division in the Democratic Party is not about any one person, or even about 2016. The rift is historical. As a growing number of people who vote Democratic count themselves as socialists or leftists, especially young Democratic voters, the contemporary party has become host to a longstanding struggle between leftists and liberals.

Conservatives have long sought to blur the boundaries between the left and liberalism.

Conservatives have long sought to blur the boundaries between the left and liberalism. Senator Joseph McCarthy tarred anyone to the left of President Dwight Eisenhower as a commie pinko. This venerable tradition of redbaiting continues to this day across the vast right-wing media landscape. But we should not make the same mistake. Distinctions between the left and liberalism matter, and they have a history. The left-liberal divide is grounded in competing political philosophies that have been developing for the last century or longer in American history.

For an excellent primer on these differences, I recommend two essays from the newly published Cornell University Press volume that I co-edited with Raymond Haberski, American Labyrinth: Intellectual History for Complicated Times.

Start with Chapter 8 by Kevin Mattson, the Connor Study Professor of Contemporary History at Ohio University who is well known in political and intellectual history circles for his many penetrating and insightful books about American liberalism. Mattson’s chapter, “Toward a New, Old Liberal Imagination: From Obama to Niebuhr and Back Again,” is a forceful essay that foregrounds the 2016 Democratic primaries. Mattson illustrates that the intellectual history of liberalism, exemplified by the illuminous theologian and Cold War liberal Reinhold Niebuhr, endowed Barack Obama (and to a lesser extent Hillary Clinton) with the right mix of hope and humility to carry liberalism forward in a way that he could support. Although Mattson is on the left end of the liberal spectrum, and although he supports some of the social democratic tendencies forwarded by Sanders, he found the Sanders campaign’s bracing, class-focused rhetoric hostile to the liberal political discourse that carried liberal reform victories throughout the twentieth century.

After Chapter 8, continue with Chapter 9, by me, titled, “Against the Liberal Tradition: An Intellectual History of the American Left.” In this chapter I largely agree with Mattson’s categories but reverse his judgment, since I argue that the major liberal reforms of the twentieth century could not have happened without a left pulling the liberal center a bit towards the left. More than that, my contribution to American Labyrinth provides a genealogy of the left that traces its origins to its late nineteenth-century adoption of Marxism and argues that the American Left has always existed in creative tension with liberalism and is in fact defined by that tension. This is a tension that will likely return to the surface in the 2020 Democratic primaries.

Haberski and I developed American Labyrinth with the following question in mind: How might the methods of intellectual history shed light on urgent contemporary issues with historical resonance? The left-liberal divide in American politics—a divide that currently defines the Democratic party’s trajectory—is just such an issue that our book tackles with gusto.

Andrew Hartman is a professor of history at Illinois State University and is currently the Fulbright-British Library Eccles Centre Scholar.