The candidate's position was clear and direct: "I have no purpose to interfere with the institution of slavery," he said. "I have no lawful right to do so."
But as president, he declared the slaves free, at least in some states, by executive order.
Abe Lincoln, flip-flopper? Or did the Great Emancipator simply evolve?
Ronald Reagan was for a woman's right to choose an abortion before he was against it, yet his shift was widely viewed as principled evolution, not craven politics.
Mitt Romney has made much the same journey, only to find himself battered by skepticism about his motives and principles. After months of attacks about position-switching from his Republican primary opponents, Romney was markedly restrained in responding to President Barack Obama's announcement this month that he was flipping from opposing same-sex marriage to endorsing it.
In politics, a mind can be a terrible thing to change.
Attack ads featuring spinning weather vanes and double-talking candidates have become a staple of American campaigns, but consultants who make those ads say the flip-flopper charge doesn't always stick — and no one has a formula to predict exactly when it will.
But there are reasons why some politicians' changes of heart strike voters as evidence of duplicity and others are accepted as the result of reasoned reconsideration — and America's cultural divide on social issues might explain why certain flip-flopper charges hit home.
"Voters tend to be fair-minded about this kind of thing," said Geoff Garin, a longtime Democratic pollster and strategist. "Voters look for obvious motive, for cravenness. You get extra demerits for being a repeat offender."
Was it flip-flopping, evolving or adapting to altered circumstance when Obama changed direction about closing the Guantanamo Bay detention camp for suspected terrorists, or about the wisdom of standing by Egyptian President Hosni Mubarak, or about whether Obama campaign officials would appear at fundraisers for super PACs?