President Obama endorsed same-sex marriage last Wednesday afternoon in a televised interview with ABC News. We asked Robert Gilbert, the Edward W. Brooke Pro­fessor of Polit­ical Sci­ence in North­eastern University’s Col­lege of Social Sci­ences and Human­i­ties, to assess the social and political implications of Obama’s announcement, which has largely been viewed as a symbolic gesture by both pundits and White House aides.

One senator called Obama’s affirmation of same-sex marriage “a watershed moment in American history.” Where does his endorsement rank among history’s most prominent presidential proclamations?

There have been a number of “watershed moments” in our history, and it’s very difficult to prioritize among them. Most of these came about very slowly. Obama’s endorsement of gay marriage last week evolved torturously over time, as did President Kennedy’s dramatic espousal of equal rights for black Americans in June 1963. The proclamations of these two leaders emerge as highly significant because both put the prestige of the presidency of the United States behind major — and controversial — social change.

Obama endorsed same-sex marriage just one day after North Carolina — the site of the 2012 Democratic National Convention — voted to pass an amendment banning the practice. How will Obama’s announcement impact voting in swing states with gay-marriage bans?

In swing states such as North Carolina, Indiana and Ohio — which Obama carried fairly narrowly in 2008 — the announcement will not be particularly popular. It seems likely to energize Romney’s base and push it to the polls. It should also intensify Obama’s support among gays and lesbians, but these gains will not be as great as those for Romney.

My overall view is that Obama’s leadership credentials were burnished here, but that he was acting primarily as a moral leader rather than as a president facing re-election.

Will Obama’s presidential legacy be defined by his skin color, his support for same-sex marriage, his role in the killing of Osama bin Laden, or something else?

I think Obama’s legacy depends, in part, on whether or not he serves two terms. If he serves only one term, the fact that he was the first African-American president will loom very large. That fact alone sent reverberations throughout the globe in 2008. If he serves two terms, however, his legacy will be broader and his race ­— although still very important — will not be as dominant.