It happened a short while ago on Meet the Press.
I'm always hesitant to put too much stock into endorsements, because, like, do they really matter that much? I guess the correct answer would be that they do matter - but only sometimes. And this feels like one of those times.
Cynics will say "Oh, he's only endorsing him because they're both black," but Powell himself put that notion to rest this morning. Obama gets the endorsement because of the "transformational" aspect of his candidacy, and because it's clearer now than ever that he is the right man at the right time for America.
Still, though, watching Powell today was really striking. To hear such an eloquent endorsement from a traditional, moderate Republican and well-respected former general is excellent news for the Obama campaign. Powell served under both President Bush and has an admittedly deep affection for John McCain. And he's voting for Barack Obama. What does that say to you?