President Obama sits down with ABC News’s Robin Roberts this afternoon for a “wide-ranging” interview at the White House. There’s a lot to talk about. But everyone wants to hear him talk about evolution. More specifically, his evolution on the issue of same-sex marriage. I and countless others have called on the president to “evolve already.” Perhaps today will be the day when Obama stands upright to declare his support for marriage equality.

As easy as we try to make it sound, making such a declaration is fraught with political peril for Obama. In an excellent piece for the “Campaign Stops” blog of the New York Times, Ross Douthat posits two explanations for Obama reticence that should be considered.

The first reason is that while the increase in public support for same-sex marriage over the last two decades has been astonishingly swift, it has not been irreversible. Instead, sudden bursts of legal momentum — mostly driven by judicial rulings, from Massachusetts to Iowa — have often prompted temporary backlashes.....

The second reason for the White House’s caution is that opinion polling has consistently understated opposition to same-sex marriage since the issue rose to national prominence. Voters who say they support it when Gallup and other pollsters come calling can behave very differently in the privacy of the voting booth.

A Gallup poll released yesterday proves Douthat's first point. Last year, 53 percent supported same-sex marriage. Today, it’s now 50 percent. Still on the right side of history but still a drop in support. Douthat cites a 2010 study by Patrick Egan of New York University that proves his second point. “[S]urvey data consistently underestimate voter opposition to legal recognition of same sex couples,” according to Patrick Egan of New York University. “The share of voters in pre-election surveys saying they will vote to ban same-sex marriage is typically seven percentage points lower than the actual vote on election day.”

This puts the president’s reticence into clearer focus. But leadership is about doing what’s right when it is neither easy nor convenient. Leadership on issues of civil rights is never easy or convenient because it requires bringing people to a just destination when they are not quite ready to get there. Still, that’s no excuse for inaction. That’s not say that Obama has ignored the inequities facing gays, lesbians and their families. He’s done more than all of his predecessors combined. But having his words match his considerable deeds would be the very definition of leadership.