When windows are smashed, shops go up in flames, looters ransack and police open fire, the collective psyche automatically clicks over to 1968 — in particular, to April, after Martin Luther King Jr. was shot down in Memphis and more than 100 American cities burst out in riots (or, as many participants preferred to call them, rebellions). Governors called in the National Guard, 43 people were killed, more than 3,000 were injured and some 20,000 were arrested. The conservative journalist Bill Whalen writes of reading “1,968” articles comparing this year with 1968.

Yes, there is something of 1968 in 2020. But the 1968 synapse oversimplifies greatly. The uprising underway now signals a vastly more popular and widespread movement reminiscent of the great outpouring of anti-Vietnam War action in October and November 1969, under the aegis of a national project called the Moratorium, which, amid outrage long in the making, cried out: Enough.

Even as the country’s largest radical organization of the 1960s, Students for a Democratic Society, broke up into warring “revolutionary” factions, the majority of war opponents, rallied by unsung leaders, turned to congenial tactics. The issue was different from today’s, but the ecumenical spirit, the resolve and the conviction about the need for a new political start were similar. Then as now, the rallies expressed both solidarity and self-interest. In 1969, with the draft in force, many in the Moratorium crowds had a huge personal stake, though many did not. Today, black protesters have the most obvious stakes, but whites in the far-flung crowds, under a broad range of leaders, are also moved selflessly and morally.

The Moratorium was widespread, politically heterogeneous, mostly middle class, largely white but cross-racial, and, contrary to President Richard Nixon’s White House propaganda, effective. On Oct. 15, 1969, in major cities and small towns across the country, some 2 million Americans opposing the Vietnam War turned out for rallies, vigils on town greens, church services, petition drives and speeches. Church bells tolled for the dead. High schoolers walked out. Black armbands appeared everywhere. Respectability was the hallmark. All of these demonstrations were nonviolent. (In front of the White House, police cracked down on some black activists.) Families were shaken.

One National Security Council official, William Watts, taking a break from writing Nixon’s forthcoming speech announcing a major escalation in the war, walked out of the West Wing and onto the lawn — only to see his wife and children march by in the antiwar crowd, each holding a candle. “I felt like throwing up,” he said later. “There they are demonstrating against me, and here I am inside writing a speech.” No comparable remarks have been heard from the West Wing of 2020. Seven months later, Watts and other staffers would resign over Nixon’s expansion of the war to Cambodia.

Another million or so antiwarriors took part in the second Moratorium, again nonviolent, except for a militant, riotous offshoot in Washington that was met with tear gas by the D.C. police and unsurprisingly ate up a lot of media space. In the White House, while professing to be unfazed, Nixon is said to have joked that helicopters should overfly the demonstrators to blow out their candles. As it happened, President Trump’s helicopters did fly overhead to disperse a nonviolent crowd this month in Washington, where earlier that day the police used rubber bullets, smoke canisters and pepper spray to clear the way for a presidential photo op in Lafayette Square in front of the White House.

The chief shock reverberating through the Nixon administration came from the protest’s sheer numbers and social breadth. Today, obviously, the issue is different and the outcomes are still under construction. The Moratoriums were explicitly antiwar; the demonstrations of 2020, under the rubric Black Lives Matter, protest police brutality against African Americans. But the outpourings rhyme in several crucial respects: the geographic and social range of the protests (2,919 as of June 10); their popularity among the larger public (in 1969 this was especially remarkable, given the fact that militant-turning-violent antiwar demonstrations were widely despised); the attention and support from mainstream politicians, clergy and the press; and the political effects, even if 2020’s are still unfolding.

Talk about widespread. Consider Corbin, home of Kentucky Fried Chicken, where six peaceful Black Lives Matter rallies took place within a week and a half: The nonpartisan mayor of this small eastern Kentuky town, Suzie Rasmus, calls herself “a centrist at heart” who was “heartbroken” at the murder of George Floyd. She spoke at a candlelight vigil. “Police participated in two of them,” she told me. “The first night, the police chief knelt in prayer. It hurts my heart and it hurts their hearts too.” According to the local paper, a few hecklers showed up but “there were far more expressions of support.” Corbin was one of America’s many “sundown towns” that once excluded blacks; in October 1919, a white mob forced the town’s black residents onto a freight train and shipped them out of town.

History rhymes, but it doesn’t repeat. In 1969, as today, new leaders came forward, new tactics were deployed, and thoughts turned to the perennial problem of what next. This year, during a presidential campaign, those plans center not only on police department reforms but on voter registration, turnout mobilization, lobbying, legislating and political campaigns. A culture of solidarity forms, perhaps partly because Americans have already rehearsed social cohesion with social distancing and mask-wearing to ward off the coronavirus. Surprising allies and defenders crop up. In 1969, no one could have imagined that the First Amendment right of demonstrators to unimpeded assembly would win the strenuous support of so many retired military leaders. One retired military official called these past few weeks “a precipice moment.” Sen. Mitt Romney (R-Utah) marched with protesters last weekend, echoing the cross-aisle reach.

What kind of effects do such outpourings have? Many, and often backstage, with relative weights that are hard to measure. The Moratorium forced Nixon to scale back “Operation Duck Hook,” a major planned escalation in Southeast Asia, which included the possible use of nuclear weapons. The operation and the cancellation were, of course, kept secret at the time.

Today, the public not only sides with peaceful demonstrators (and against looters and vandals) but agrees that police practices must be reformed, even that our criminal injustice system must be “reimagined,” though few want to see the police wholly disbanded. All manner of reforms are publicly proposed and vigorously debated at local and state levels — and just as vigorously resisted. The unspoken motto is: Try reforms at home. Results may vary.

Mood comparisons are of course imprecise, just as political contingencies are incalculable, but if anything, the hope for change is greater today, even as the president digs in. The presumptive Democratic nominee for president, Joe Biden, embraces the spirit of the protest if not all the measures that activists put forward. The election campaign will be recast, at least for a while, as a fight between Trump’s contempt and Biden’s compassion; between Trump’s bombastic ignorance and Biden’s respect for professional knowledge; between Trump’s paranoid conspiracy theories and Biden’s declaration: “We must urgently root out systemic racism, from policing to housing to opportunity”; between disrespect and respect for human rights.

Reform efforts will not flow evenly or sweetly. Provocations from the right, and the administration, and possibly a few freelance rioters, may tilt the course of events. Some backlash is likely, although it is not yet showing up in the polls. You’d have to be smoking something extra strong to be confident that major police revamps are about to sweep the country. The 2022 midterms will open up new opportunities for right-wing panic and vengeance. Defenders of armed federal intervention, like Sen. Tom Cotton (R-Ark.), will not go quietly. History proceeds by fits and starts. But in a way almost no one imagined possible one month ago, it proceeds.

Twitter: @toddgitlin