Tuesday night, Barack Obama kept the second half of his post-primary speech to his usual message, hammering home the idea that he's the only presidential candidate who can bring change and hope to the U.S. But before that, he offered some unusually strong, direct attacks on his opponent, Hillary Clinton.

Maybe it was a sign of a less-than-blockbuster night for Obama, or perhaps he knew what was not yet public when he spoke -- that Clinton had won the night's biggest prize, California -- but whereas in her speech Clinton had refrained from attacking Obama, in his he showed little mercy.

The offensive came subtly at first. Cloaked. "This isn't about me and it's not about Senator Clinton. As I've said before, she was a friend before this campaign, she'll be a friend after it's over," Obama said. "I respect her. I respect her as a colleague. I congratulate her on her victories tonight. She's been running an outstanding race."

Then came the turn.

"But this fall, we owe the American people a real choice," Obama said.

"We have to choose between change and more of the same. We have to choose between looking backwards and looking forwards. We have to choose between our future and our past.

"It's a choice between going into this election with Republicans and independents already united against us or going against their nominee with a campaign that has united Americans of all parties...

"[I]f I am your nominee, my opponent will not be able to say that I voted for the war in Iraq, because I didn't, or that I gave George Bush the benefit of the doubt on Iran, because I haven't, or that I support the Bush-Cheney doctrine of not talking to leaders we don't like, because I profoundly disagree with that approach.

"And he will not be able to say that I wavered on something as fundamental as whether or not it's OK for America to use torture, because it's never OK."

"That is the choice in this election."