Steffan Schmidt was a graduate student at Columbia University in the late 1960s, and he remembers the tear gas that sifted through the window when he was taking his oral examination for his PhD at the very moment his fellow students were demonstrating, and being arrested, outside.
"There was Vietnam and racial tensions," said Mr. Schmidt, now a political scientist at Iowa State University. "It was a very divisive and disruptive time."
William Cohen was the mayor of the small Maine city of Bangor when he won election to the House of Representatives and, as a freshman Republican, was assigned to the committee considering the impeachment of President Richard Nixon.
"When I voted with the Democrats on the mere matter of a letter to the president, all hell broke loose," Mr. Cohen, who later was elected to the senate and eventually served as Secretary of Defence, recalled in an interview. "Later we had bomb threats and I ended up in a basement. I had to get protection for my kids. My constituents told me I was a traitor and threatened to throw me out. The passions and tensions were so high you cannot imagine them."
The United States has had moments of disunity before the election of Manhattan businessman Donald Trump. And while the divisions that are playing out across the country are real, they are by no means unique.
"We have been this divided before," said Alasdair Roberts, who teaches at the University of Missouri's Truman School of Public Affairs and is author of Four Crises of American Democracy, which is to be published by Oxford University Press nine days before the inauguration of Mr. Trump.
"We have had recurrent times when people think there is something wrong with democracy. And in each of these phases, a lot of people are unsatisfied with the conventional wisdom of how government is supposed to work, followed by a period of political protest and unrest."
Indeed, there have been great divisions even within the life memory of Mr. Trump himself. The civil-rights movement reflected divisions between black and white. The Vietnam War produced divisions within families. Watergate hardened, and expanded, divisions between Republicans and Democrats.
The difference is that the Trump phenomenon revealed profound divisions not along party nor on generational lines but along class lines. Mr. Trump identified deep disquiet and despair among white working-class Americans and then harnessed the power of that discontent to defeat former Secretary of State Hillary Clinton in a campaign that underlined class divisions rather than papered them over.
"On every possible issue and in every possible dimension, Americans are divided," said John Dick, who heads CivicScience, a Pittsburgh-based market research company. "There's almost nothing of consequence we agree on. We are divided by geography, by socio-economic dimensions. There's even an unusual division between people who are engaged in current affairs and people who are passive. And remember that half of Americans didn't even vote. That itself is a division."
But for all the divisions Americans face, they are united in the belief that this is a period of unusual tension. Perhaps it is the immediacy of the presidential election, or the passions stoked by barrage of negative television advertisements, the sharp exchanges in the three presidential debates and relentless social media. Perhaps it is simply a lack of perspective.
"We've had divisive periods before," said David Greenberg, a Rutgers University historian and author of biographies of Mr. Nixon and Calvin Coolidge, who was president between 1923 and 1929. "There were times in the late 1960s when people thought a revolution was coming, and that society was about to be overturned. And in the 1930s, in the wake of the Depression, there was a sense that the system was in crisis and there were questions about the viability of democracy."
There were many other divisions in a country that once conducted a Civil War – a conflict "that was prompted by a presidential election," argues Grinnell College historian Sarah Purcell in reference to the 1860 campaign won by Abraham Lincoln.
The race of 1912 – which resulted in the election of Woodrow Wilson and the defeats of president William Howard Taft, former president Theodore Roosevelt and Socialist crusader Eugene V. Debs – convinced many, especially women and blacks excluded from the franchise, that politics was run solely by the rich.
"People forget that we are divided most of the time in America," said Michael Kazin, a Georgetown historian who was expelled from Harvard, where he was the chairman of the radical Students for a Democratic Society (SDS) in 1969, and who later was a celebrated biographer of the 19th-century populist hero William Jennings Bryan, a three-time presidential candidate. "In 1896, people thought Bryan was an anarchist."
But more recent divisions still have resonance.
"The Millennials don't understand that we were divided even more in the 1960s," said former Pennsylvania governor Tom Corbett, who finished high school in 1964. "What's new about this is instant communication. There's no time for reflection. Nor do people remember or understand history the way they used to."
Indeed, the divisions of that period are still vivid – and searing.
"The 1960s were not only full of division but there was also violence," said Todd Gitlin, a New Left activist who was president of SDS and who in 1965 organized the first mass protests against the Vietnam War. "More people were being killed: civil-rights workers, black people. More people were being beaten up by police. You had war veterans whose boys didn't want to got to war, and there were arguments and ruptures. Families were torn apart. There were screaming fights and disownings."
In his poem Story, from his debut on the poetry scene in 1956 – a year of unusual upheaval produced by the Suez War and the Soviet suppression of the uprising in Hungary in the middle of an otherwise tranquil decade – the late Leonard Cohen wrote, "It is important / to understand one's part in a legend." And so it is equally important to understand the divisions of the past, and to measure them against the divisions of contemporary life, which seem so sharp and so urgent.