One virtue of the crowded, often compelling narrative in Radicals in American: The U.S. Left Since the Second World War is that it makes Bernie Sanders appear to be one of the more sensible, as well as most consistent, leftists in America.

As historians who yearn for a bigger and stronger radical movement, authors Howard Brick and Christopher Phelps want to separate the good left with its emancipating, altruistic ideas from the bad left that glories in self-destructive and sometimes lunatic rhetoric and behavior.

Born in 1941, Sanders got “radicalized” at the University of Chicago. He then spent much of the ’60s fighting to integrate neighborhoods and schools and trying to emulate such social-democratic, pro-union icons as Michael Harrington and Martin Luther King Jr. instead of utopian tyrants like Mao Tse-tung and would-be urban guerillas like Eldridge Cleaver. During the annus mirabilis of 1968, he moved to Vermont, which was fast becoming a mecca for back-to-the-land lefties. There, he organized an anti-corporate third party and began running, quite successfully, for political office—mayor of Burlington, a seat in the House, and then one in the Senate.

Today, when Sanders addresses throngs of admirers all over America and gets interviewed on national TV, his message is much the same as he delivered to small-town New Englanders almost 35 years ago. “If we wanted to, we could wipe out economic hardship almost overnight,” he told a Vermont paper back in 1971. “We could have free medical care, excellent schools, and decent housing for all. The problem is that the great wealth and potential of this country rests with a handful of people …”

Brick and Phelps contend that this vision of economic democracy, of a welfare state that would resemble Norway’s, has always been too constricted. Their good left was and remains a “movement of movements,” From the ’60s to the mid-’70s, radicals slipped the bonds of a labor-centered ideology and spawned the Black Panthers, the Gay Liberation Front, a new feminist insurgency, the American Indian Movement, Earth First!, and the largest anti-war movement in U.S. history. This “remarkable crescendo,” they write, “widened and diversified the radical agenda, resulting in much richer ... visions of freedom, equality, and community.”

Of course, even the good left included some bad, or at least severely deluded, actors. Weathermen and Weatherwomen equated revolution with running amok in the streets, hectoring teenagers to stop going to school, and bombing a men’s room in the Capitol. One of them was Shin’ya Ono, who happened to be Yoko’s cousin. Disciples of Mao and Stalin created a handful of “new Communist parties,” none of which figured out how to translate their “otherworldly and esoteric” prose into something approaching the language Americans actually speak.

By the time Ronald Reagan moved into the White House, radicals of every stripe were firmly on the defensive, no longer confident of becoming the midwives of a nation transformed. Up to this point, Brick and Phelps tell a convincing story stuffed with vivid details about individual activists, both famous and obscure, and their assault on “the System” whose “practical effects … were both liberating and self-marginalizing.”

Yet when their narrative reaches the ’80s and ’90s, they wander from worthy cause to cause, failing to confront or explain the left’s rapid decline. The nuclear freeze, Jesse Jackson’s runs for president, the campaigns against apartheid and Reagan’s backing for the Nicaraguan Contras, and the push for “global justice” that, in 1999, erupted in the “Battle of Seattle” all had their moments of growth and media frenzy. But, taken together, they did nothing to release the left from the periphery of American politics.

Whatever its shortcomings, the New Left had made a powerful moral argument about three inescapable problems that touched the conscience and/or self-interest of most Americans: legal racism, the war in Indochina, and the inequality of women. Nothing that big or vital emerged during the last two decades of the 20th century.

Some radicals who should have known better mistook the endurance of activism in the Reagan era for political influence. The authors approvingly quote Noam Chomsky declaring in 1988, “This country is more dissident now than at any time I can remember, more so than during the Vietnam War.” It was not the first time the great linguist had been a horrendously unreliable guide to current events. A decade before, Chomsky apologized for the genocide committed by the Khmer Rouge. According to Brick and Phelps, he blamed the murder of 1½ million Cambodians on the “mass psychosis induced by years of U.S. carpet-bombing.” By that logic, the Holocaust was really the fault of the French and British who demanded that the Germans pay billions of marks in reparations after their defeat in World War I.

However, American radicals are not necessarily fated to remain forever on the margins, plagued by their fragmented passions and a recurring inability to grasp the obvious. Since 2008, there has been a revival of sorts, one the authors note in passing at the end of their book. The Great Recession, Barack Obama’s thrilling ascent to the presidency (which spurred a new generation of activists, even if some later soured on his performance in office), the short-lived yet catalytic uprising that was Occupy, and the demand for a $15-an-hour minimum wage have combined to turn economic inequality into an issue no one in public life can ignore. The left may still be a “movement of movements”—some of which, like LGBT activism and BlackLivesMatter, have also been surging of late. But for the first time in four decades, it now has an overriding reason for being—one that, as Sanders is demonstrating, has appeal beyond the usual suspects.

Brick and Phelps conclude their book with a wise reflection on what the left has achieved—and manifestly failed to accomplish—over the past seven decades. “Successes … in extending respectability and belonging to women, people of color, gays and lesbians, the disabled, and other once blatantly disparaged groups have been impressive,” they write, “but they are incomplete and cannot be separated from other signs of a country turning ever less egalitarian and democratic.”

Bernie Sanders will not become the next president or even the Democratic nominee. Neither his party nor his country have changed enough to allow an angry, white-haired Jewish radical to become the most powerful person in the world. But if his fellow leftists follow his rhetorical lead, preferably with a touch of humor, they might yet secure themselves a future more promising than their recent past.

Michael Kazin is co-editor of “Dissent” and teaches history at Georgetown University. His most recent book is “American Dreamers: How the Left Changed a Nation.”