We are in a populist moment, as political strategists of every ideological strain recognize. No leader and no party has harnessed this populist energy, though it surges around every political issue, every election. Our politics will become increasingly convoluted until someone captures and focuses this energy, giving the populist movement a vision for the future consistent with a widely received version of the past. This is a sweet populism, one that affirms American society and institutions.

Sweet populism is a peculiarly American species, organized around a version of the country's history that is positive and incomplete; stresses the importance of self-reliance; seeks to remove obstacles to individual empowerment when they emerge; and aims any anger it produces at those who deny the essential goodness of the American idea.

We are in a populist moment, as political strategists of every ideological strain recognize. No leader and no party has harnessed this populist energy, though it surges around every political issue, every election. Our politics will become increasingly convoluted until someone captures and focuses this energy, giving the populist movement a vision for the future consistent with a widely received version of the past. This is a sweet populism, one that affirms American society and institutions.

Sweet populism is a peculiarly American species, organized around a version of the country's history that is positive and incomplete; stresses the importance of self-reliance; seeks to remove obstacles to individual empowerment when they emerge; and aims any anger it produces at those who deny the essential goodness of the American idea.

In short: Sweet populism concerns what is necessary for retention not transformation, for progress rather than revolution, for love of what is American and suspicion of anything that threatens the independence and self-rule at the heart of the American story.

The sweet populism of Ronald Reagan, for instance, emphasized a historical account of progress that was threatened by anti-American ideas of collective guilt and collective responsibility. Reagan's populism elevated the social over the political because Reagan understood "the people" to be separate and above their governments.

Jimmy Carter's sour sense of limits, by contrast, conflated the public and the government, giving his policies a paternalistic and intrusive quality. When Reagan declared that the problem wasn't the people but the government, he was affirming the essential goodness of the American story and its citizens. Americans, he believed, can be trusted to run their lives.

Tea party participants seem to think of themselves as heirs to Reagan's version of populism, and they are half right. They stress individualism and self-rule, and they hold up the Constitution as not only the defining governing document but as proof of the superiority of the American system. Unable yet to express the dynamic spirit of American history as a story of evermore freedom, tea party advocates seem trapped by their own historical account rather than empowered by it.

Successful American populism is always a creative reaction. This populism responds to concentrations of power—economic or political—that hinder individual freedom, producing instead a new and updated expression of the basic American ideals.

Uninterested in equality as an abstract ideal, this populism opposes the forms of inequality that threaten freedom. In the process, this populism articulates a hopeful, democratic and generous vision of the future. If Republicans are going to harness today's populist energy, it will be through this creative reaction, this reformulation of the American story that fits the moment.

On the other side, progressive media outlets such as Mother Jones and the Nation have been calling for a forceful populist message that crystallizes a subterranean unrest produced by income inequalities. The keynote of this species of populism is resentment—the standard expression of European populism for two centuries.

Organized resentment requires anger, and anger requires villains. The vilifying of the billionaire Koch brothers provides a human target, helping stir the emotional energy necessary to pursue deeper structural change. Whatever the transformation of American society looks like for progressives, their policy takeover requires resentment and anger that endorses top-down intervention into the very institutions of daily life. The positive expression of resentful populism is social justice, a vague moralism that allows lawmakers, bureaucrats and others to disregard the sanctity of long use as they try to alter these basic social institutions.

President Obama's populism appears to affirm American values but actually seethes with resentment toward middle America. The president constructs a progressive and reassuring historical narrative, drawing Abraham Lincoln andTheodore Roosevelt into an arc of history that leads to the present age of social awakening. Yet Mr. Obama, in candid moments, lets slip the bitterness underlying his philosophy, as during the 2008 presidential campaign when he maligned those who "cling to guns or religion" or when he promises a "fundamental transformation" of American society. Mr. Obama's species of populism will be remembered for his famous "you didn't build that" dismissal in 2012 of those who have founded successful businesses—an expression of disdain for the defining belief of sweet populism.

The problem for progressive populism is that it rejects as untrue and immoral the most powerful American myth: the self-governing person, happily ensconced in family, church, community and work. It is not merely resentment toward the 1%. In the end, progressive populism reveals its contempt for all Americans who continue to believe the most seductive social myth in modern history.

Right now, populist voices on both the left and right have failed to channel the energy of a frustrated but largely voiceless middle. America is still a nation in which equality serves the ideal of freedom rather than the other way around. What is needed now is a new mythmaker who can describe the future of freedom.

Mr. McAllister, a professor of public policy at Pepperdine University, is co-editor of "Why Place Matters: Geography, Identity, and Civic Life in Modern America" (Encounter Books, 2014).