Liberals have more problems than one can comfortably count these days, but the essential one is this: fewer than one in seven Americans trust the government “to do what’s right almost always or most of the time,” an all-time low since pollsters began asking the question in 1958. This is approximately the same anemic percentage as those who, questioned in a previous poll, expressed confidence in the government’s “ability to stand up to vested interests.” Barack Obama’s hyper-cautiousness and misguided deficit obsession notwithstanding, if liberals cannot change those numbers, they cannot win.

Liberal politics, Michael Walzer observes, is difficult “because it offers so few emotional rewards…it lacks warmth and intimacy.” Without universal foundations—Lionel Trilling termed it “a large tendency rather than a concise body of doctrine”—liberalism can offer only narratives of sacrifice and common purpose, ones that can often be trumped by the tales of the right, which frequently combine libertarianism with jingoism, fearmongering and other easily pushed emotional buttons that tend to drown out the more idealistic liberals’ homilies. As Richard Hofstadter feared nearly sixty years ago, “In a populistic culture like ours, which seems to lack a responsible elite with political and moral autonomy, and in which it is possible to exploit the wildest currents of public sentiment for private purposes,” it would be “at least conceivable that a highly organized, vocal, active, and well-financed minority could create a political climate in which the rational pursuit of our well-being and safety would become impossible.” Sound familiar?

Ironically, it is at moments when liberalism is most difficult to practice that its defense is most desperately needed. As I argue in my new history, The Cause: The Fight for American Liberalism From Franklin Roosevelt to Barack Obama, while liberal policy prescriptions certainly change over time, their inspiration has not. To be a “liberal” is to be a child of the Enlightenment, to stand firm on behalf of the foundational freedoms of thought and expression. Liberalism insists that individuals take hold of their fate and shape it according to the values of liberty and equality, while being fully aware that the two must always coexist in tension with each other. While the word “liberal” has come to imply many ideas and commitments over the past two centuries, only those that honor what John Kenneth Galbraith called “the emancipation of belief” are worthy of it. Liberalism’s guiding spirit can be found in the words of Immanuel Kant, who in 1784 proclaimed: “Sapere aude! [Dare to know!] Have courage to use your own understanding!”

The liberals who founded America invented a new form of government based on these precepts. They aspired to create what Thomas Jefferson called a nation of “natural aristocrats,” a term they associated not with family lineage but with what historian Gordon Wood defines as the qualities of “being reasonable, tolerant, honest, virtuous and candid.” Further, they implied “standing on elevated ground in order to have a large view of human affairs, [and] being free of the prejudices, parochialism, and religious enthusiasm of the vulgar and barbaric.”

Moved by the misery of the Depression, and driven to action by the failure of private enterprise to lift the country out of it, Franklin Roosevelt expanded this definition. Opposed to what he called “the conservative party,” which—then as today—“honestly and conscientiously believes” that “in the long run, individual initiative and private philanthropy can take care of all situations,” he deployed government resources, through the “militant liberalism” of the New Deal, to protect people from “disasters once considered inevitable, to solve problems once considered unsolvable.”

By 1934 Democrats held more than 70 percent of the House and Senate. Under FDR’s leadership they nearly doubled their percentage of the popular vote in presidential elections, winning five in a row—a feat neither party has matched before or since—and nine out of ten Congressional elections as well. Roosevelt achieved these victories despite a decidedly ambiguous record on the economic challenges he inherited. But as historian Lizabeth Cohen suggests, the New Deal “should be measured less by the lasting accomplishments of its reforms and more by the attitudinal changes it produced in a generation of working-class Americans who now looked to Washington to deliver the American dream.”

Ronald Reagan’s transformation of political discourse in the opposite direction was in many respects the mirror image of Roosevelt’s accomplishment. If both presidents met with mixed success in policy terms, both nevertheless were able to reshape political culture because the optimism and self-confidence of the visions they offered captured the imagination of a majority of Americans, particularly the young.

If their fortunes are ever to revive, liberals must find a way to recapture this simultaneously militant and optimistic spirit. The “larger message” for what Roosevelt called “the liberal party” was a clear and simple one: “As new conditions and problems arise beyond the power of men and women to meet as individuals, it becomes the duty of the Government itself to find new remedies with which to meet them.” Add to this John Dewey’s precept that “government should regularly intervene to help equalize conditions between the wealthy and the poor, between the overprivileged and the underprivileged,” while acknowledging Reinhold Niebuhr’s prescient call for “humility” in all such undertakings, and you have a concise, compelling statement of what it means—then as now—to call oneself an “American liberal.”

When liberals lose confidence in their ability to lead Americans toward the fulfillment of this vision, they lose their reason for being liberals. If the history of liberalism has a single lesson to teach us, it is that what liberals have to fear most—far more than conservatives—is fear itself.