When the Democrats hold their national convention in Charlotte, N.C., this week, the party platform is expected to endorse same-sex marriage. This historic stride, however, isn’t without precedent. In fact, a step in this direction was taken 40 years ago in South Florida.

In 1972, three years after the Stonewall riots helped launch the movement, gay rights entered the world of presidential politics. Gay liberationists, allied with leftists, anti-war protestors and second-wave feminists, found a friend in the Democratic presidential nominee, George McGovern.

The 1968 convention had ended in chaotic confrontations between activist “yippies” and Chicago police. Fearing a repeat at the 1972 convention in Miami Beach, party leaders made changes that included more diversity in delegate selection. The party pledged to make “special efforts to reach women, young persons, minorities and others who have been shut out of the process.” This included homosexuals.

In February 1972, the National Coalition of Gay Organizations met to forge a united homosexual front. They crafted a gay rights platform that called for an end to “discrimination in employment, housing, public accommodations and public services,” an initiative that would make national headlines — once again, in South Florida — five years later with Anita Bryant’s Save Our Children campaign. Their demands also included the repeal of laws restricting same-sex marriage and an end to the immigration policy that barred homosexual aliens from the United States.

The New York delegation sent nine affiliates of the Gay Liberation Front to participate in the Democrats’ platform deliberations. Ultimately, the party’s platform committee rejected the gay coalition’s demands by a vote of 54 to 34.

Despite this defeat, the process placed South Florida at the center of the nation’s homosexual debate. At the Miami Beach Convention Center, Democratic delegates heard activists Jim Foster and Madeline Davis speak on behalf of the minority plan on sexual orientation — the first time that someone advocated, in front of TV cameras on the floor of a presidential convention, for the homosexual cause.

Activists also celebrated another victory. The political and social momentum led gay liberationists to file a successful federal suit for the repeal of a decades-old Miami Beach ordinance that outlawed cross-dressing.

Coincidentally, the 1972 Republican National Convention was also held in Miami Beach. During that gathering, gay activists staged a protest that resulted in at least 20 arrests.

When President Barack Obama announced his “evolution” on same-sex marriage in May, it represented a shift from a campaign of “hope” to one grounded in “promise.” With the same-sex marriage debate still roiling, one thing seems certain: We are watching history in motion.

Julio Capó Jr. teaches history at the University of Massachusetts, Amherst.