On Nov. 17, 1968, Albert Shanker, a tough Queens-bred union president, stood next to New York City’s patrician mayor, John Lindsay, to announce a settlement to a crippling teacher strike that had thrown a million students out of New York City public schools for weeks on end. The divisive strike laid bare long simmering tensions within American liberalism over unions, education and race. Almost a half-century later, the evolution in liberal attitudes that the strike symbolized created vulnerabilities that a very different son of Queens, Donald Trump, exploited in his rise to the presidency.

By the late 1960s, after years of frustration with vicious white resistance to school integration, many African-American leaders supported the creation of a black-controlled local school district in the low-income Ocean Hill-Brownsville section of Brooklyn. The idea was that the district would hire more minority schoolteachers in order to provide role models for students and adopt a curriculum that was culturally affirming.

A firestorm erupted, however, when the local school board (then known as the governing board) sent a telegram to 19 unionized educators indicating that the board “voted to end your employment in the schools of this district.” The list included 18 white educators and one black teacher, mistakenly included, who was immediately reinstated once the error was discovered. A hearing by a retired African-American judge hired by the board, Francis Rivers, found that there were no credible charges against the teachers. But Rhody McCoy, the Ocean Hill-Brownsville local superintendent, told The New York Times, “Not one of these teachers will be allowed to teach anywhere in the city. The black community will see to that.” To protest the terminations, teachers throughout the city began a series of strikes shutting down the nation’s largest school system from early September through mid-November.

Many wealthier liberals, including Mayor Lindsay and McGeorge Bundy, the president of the Ford Foundation, joined with black activists like Stokely Carmichael in what they saw as an important effort to better the opportunities of black students. They argued that the union was standing in the way of teacher diversity. Two years earlier, Carmichael suggested that integration was “a subterfuge for the maintenance of white supremacy” because it “reinforces, among both black and white, the idea that ‘white’ is automatically better and ‘black’ is by definition inferior.”