The Democratic Party Presidential primary is now heating up as a two-person race between two evenly matched candidates, both of whom declare themselves and not their adversary to be a “progressive.”

Bernie Sanders has declared that “You can be a moderate. You can be a progressive. But you cannot be a moderate and a progressive.”

Hillary Clinton has expressed amusement that Sanders considers himself the “gatekeeper on who’s progressive,” defending her consistent claim that “I’m a progressive who likes to get things done.”

Which of these public figures is right? Who is truly a progressive? The answer is that both are partially right and partially wrong, and both can lay legitimate claim to the mantle of progressivism.

The term “progressivism” entered American political discourse at the turn of the 20th century. So-called “Gilded Age” America was a very different place from the pastoral republic envisioned by Jefferson and the framers of the Constitution. It confronted major challenges associated with industrial capitalism — rising inequality, displacement, deskilling, and disciplining of workers, and a proliferation of health and safety problems associated with untrammeled free markets. It also confronted major challenges associated with immigration, cultural pluralism, urbanization, and the rise of a science-based economy. Turn-of-the-century progressives sought to harness new technologies and institutions, and also to solve the problems these caused. These progressives were reformist and centrist, and they rhetorically cast themselves as opponents of both conservatism (“backward looking” rather than “progressive”) and radicalism — at this moment the Populist Movement and the Socialist Party of Eugene V. Debs were quite powerful, particularly in certain sections of the country.

There is a complex but also fairly straight line linking early Progressives such as Herbert Croly, Walter Lippmann, Robert M. LaFollette, and Presidents Woodrow Wilson and Theodore Roosevelt, to FDR’s New Deal, Harry Truman’s Fair Deal, JFK’s New Frontier, LBJ’s Great Society, and the “third way” pioneered by President Bill Clinton, as inspired by the Democratic Leadership Council and its Progressive Policy Institute. This is the Progressivism extolled by E. J. Dionne, Jr., in his 1996 They Only Look Dead: Why Progressives Will Dominate the Next Political Era. It is likely the progressivism embraced by the Obama administration, despite Obama’s early rhetorical flourishes.

Hillary Clinton is a “progressive” in this mold — centrist, moderate, anti-radical but reformist, pragmatist, and mainstream-Democrat. She is the kind of “progressive” who is a corporate liberal — the kind that is not against corporate capitalism but seeks to sand off its edges; the kind that regards corporations and moneyed interests as legitimate interlocutors, and indeed institutions that have what political scientist Charles Lindblom once pejoratively called “a privileged position.”

Bernie Sanders is not a “progressive” in this sense. Sanders has remained outside of the orbit of the Democratic Party mainstream, and indeed he proudly calls himself a “democratic socialist.” Sanders advocates major structural transformations of capitalism, and calls for a “political revolution”—a peaceful revolution to be sure, via the normal institutions of representative democracy, but a revolution nonetheless, based on the mobilization of millions of workers, the poor, and others who have been largely disenfranchised and who have suffered through 30 years of economic insecurity and declining real wages.

But Sanders is a “progressive” in the sense of Henry Wallace’s Progressive Party candidacy for the Presidency in 1948. This is a more robustly left progressivism, which seeks to incorporate the radical legacies and impulses of turn-of-the-century populism and socialism, and the protest movements associated with antiwar struggles, civil rights struggles, and gender and sexual liberation struggles. This “progressivism” is more radical in its critique of the injustices of our society, and in its vision of a more just society. It is not revolutionary in the Bolshevik sense. But it is linked to the radical labor movements of the 20th century, some of which did involve important Communist organizers and surely involved many self-styled socialists and even Marxian socialists. Sanders is a man of what the late Michael Harrington, the founder of Democratic Socialists of America, called “the democratic left.” He represents a political tendency linked to some of the more radical elements of the labor movement, and such journals of opinion as Dissent, In These Times, The Progressive, The Nation, Mother Jones, and Jacobin.

Sanders is correct that Clinton is not a “progressive” in this sense. She is a centrist, a moderate, an establishment figure. A corporate liberal.

Clinton is correct that Sanders is not a “progressive” in the sense of The Progressive Policy Institute. He is a leftist, a radical of sorts — though one who has held elective office for over a quarter-century — an independent and something of an anti-establishment figure. He is a democratic socialist. Or perhaps a social democrat. Or a left liberal.

Thus they are both right. For “progressivism” is a complex identity with a contentious history.

What might we say about this semantic dispute, beyond clarifying history and the meaning of terms?

For one thing, that while in some ways the differences between the two “progressivisms” are important — especially regarding banks and major financial institutions, and on the morality of extreme economic inequality — in many ways the differences are not that great.

Both versions of “progressivism” lay claim to the New Deal, though Sanders places more emphasis on the insurgencies and mass movements that brought it about, and on some the more visionary ideas, such as national health insurance, that never succeeded.

Both value science, human rights, and a democratic state that addresses the public problems of society.

And both represent a serious commitment to public reason, and public life, that is anathema to the Republican Party and the right-wing forces that control it. Indeed, “progressivism” in either variant can be defined in part by the fact that it arouses the vehement hostility of the conservative movement.

It is a good thing that the debate about the future of the Democratic party centers on the claim to being a “progressive.” That a major Democratic contestant for the presidential nomination is a woman is surely something to celebrate, and for some it is even a sufficient reason to support Clinton. And indeed, in very complicated ways, Clinton has thus far been able to capture much of the support of feminist and African-American activists (though this is being contested: see the many critical responses by African-American leftists to recent pieces by Ta Nahesi Coates in The Atlantic, and by left feminists to Katha Pollitt’s recent piece in The Nation).

But the fact that the leading “establishment” candidate of the party is a self-styled “progressive” is nothing new, and in recent history, at least since the 1990’s, Democrats have followed the lead of Bill Clinton in claiming the mantle of “progressive.”

What is novel is that this candidate faces an opponent who lays legitimate claim to the more radical version of progressivism, and who celebrates the history of democratic socialism, and the labor movement, and poor people’s movements, and other protest movements of the past, and who calls for a “political revolution” against a system “rigged” by money and power.

The Sanders campaign did not arise out of thin air. It draws on a history of ideas and networks on the Democratic left, and also draws on the rhetoric, and some of the impulses and networks, of the Occupy movement. At the same time, it has taken the punditry by surprise, and it has succeeded, at least for now, in shifting public discourse to the left. This is a major accomplishment, and represents something very novel indeed, something that this country arguably has not seen for at least a half-century.

For this reason, I support Sanders. It is doubtful that he can be a viable candidate in the general election, even given the extremism and idiocy of the current Republican primary. It is even doubtful that he can defeat Clinton in the Democratic primaries. But indeed to some extent it is because I consider the latter doubtful that I am comfortable supporting Sanders now. I prefer either version of “progressivism” to the reaction that is promised by the Republicans, and I can comfortably support Sanders now, since I believe that his campaign can strengthen the party in the general election to come, and can also have long-term effects on its future. And if the campaign picks up steam, who knows where it might lead?

Can either version of “progressivism,” or more likely some combination of them, bring about major reforms of the current system, or ambitious responses to climate change, or a more fundamentally egalitarian or just society? Here I remain deeply skeptical, for reasons outlined in my 2002 book The Poverty of Progressivism. The Sanders campaign would seem to give the lie to that book’s arguments, by demonstrating the vitality and richness of a left progressive revival. But appearances can be deceiving, and I remain skeptical. At the same time, the Sanders campaign offers a unique and precious opportunity for left progressive ideas to shape public debate, and perhaps even for these ideas to propel a decent, intelligent, and passionate democratic socialist to the White House. It is an opportunity worth supporting, and at this moment in time, a “risk” worth taking.

And so while I do not agree with Sanders that Clinton is no progressive — and while I believe that in most ways Sanders is more “moderate” than some of his rhetoric indicates — I prefer his progressivism, now, to Clinton’s. This may change as the things unfold (if Hillary Clinton wins the primary, as I expect she will, I will support her with enthusiasm — she is the first woman in the history of the United States to approach the presidency). What will not change is my belief that, however one interprets “progressivism,” and whatever its limits as a political label or vision, it is infinitely preferable to the regressivism that is promised by the Republicans.