The debate, sponsored by The Times, CNN and Politico and held at the Kodak Theatre in Hollywood, was the first one-on-one meeting between Clinton and Obama. It was also the last before Democrats in 22 states, including California, vote Tuesday.
The gravest distinction came on the war, which loomed large as an issue as the presidential race began but has gradually diminished in the Democratic contests. With the war again the focus, the race reverted to the campaign's purest distillation: Clinton's experience against Obama's judgment.
As she has before, Clinton refused to apologize for voting in the fall of 2002 to give President Bush the authority to use military force against Saddam Hussein. At the time, Obama came out strongly against the war, so it looms as one of the key distinctions between the two. Their Senate votes on war-related funding since Obama was elected in 2004 have been similar.
"I think I made a reasoned judgment," Clinton said in defending the vote. Then she tried to pin the blame for the war on Bush: "Unfortunately, the person who actually got to execute the policy did not."
Twice Clinton insisted that it was time to focus on what the country would do "going forward" -- in effect, leaving behind the discussion over the war vote. She cited Sen. John McCain's criticism of Democratic desires to leave Iraq as proof that she meant to pull American troops out.
"It will be important, however, that our nominee be able to present both a reasoned argument against continuing our presence in Iraq and the necessary credentials and gravitas for commander-in-chief," she said. "That has to cross that threshold in the mind of every American voter."
Obama, however, insisted that Clinton's authorization vote defined who would run the strongest race for the White House in November.
"I will be the Democrat who will be most effective in going up against a John McCain -- or any other Republican, because they all want basically a continuation of George Bush's policies -- because I will offer a clear contrast as somebody who never supported this war, thought it was a bad idea," Obama declared.
He directly took up Clinton's implicit criticism of his "gravitas."
"Sen. Clinton mentioned the issue of gravitas and judgment," he said. "I think it is much easier for us to have the argument when we have a nominee who says, 'I always thought this was a bad idea, this was a bad strategy.' "
Later, he said of the upcoming fight with the eventual Republican nominee, "That is an argument that I think we are going to have an easier time making if they can't turn around and say, 'But hold on a second, you supported this.' "
Despite that disagreement, and a few others on smaller policy differences, the two candidates treated each other largely with deference. Unlike Wednesday's Republican debate at the Reagan Library, where John McCain and Mitt Romney glared through clenched-jaw disagreements and impugned one another's integrity, the New York and Illinois senators sat side by side and behaved as though a cross word had never come between them.
There were many uses of the word "we" -- as though the candidates were already presenting a united front against the Republicans. Each took pains to criticize McCain, President Bush and Republicans in general as much as the other.
From the opening words, they seemed intent on dispelling any lingering shadows from the bitter South Carolina contest.
"I was friends with Hillary Clinton before we started this campaign. I will be friends with Hillary Clinton after this campaign is over," Obama said.
Clinton returned the sentiment. "The differences between Barack and I pale in comparison to the differences that we have with the Republicans," she said, before mildly mentioning a few of the Democratic differences.
And she alluded to the jointly historic nature of their effort. Wednesday's withdrawal from the race of former North Carolina Sen. John Edwards meant that either a woman or an African American was in line to be the next Democratic presidential nominee.