Sen. Hillary Clinton on Tuesday turned the second day of the Democratic National Convention into a celebration of her historic presidential campaign as a breakthrough for women, but she left no doubt that she's foursquare behind Barack Obama as her party's nominee for the presidency.

After a video tribute to her long campaign against Obama, Clinton walked onstage, introduced by her daughter, Chelsea, who called her “my hero and my mother.” Together they faced a sea of waving white signs scrawled with the word “Hillary” in blue.

Declaring herself “a proud supporter of Barack Obama,” Clinton said, “Whether you voted for me or voted for Barack, the time is now to unite as a single party with a single purpose. We are on the same team, and none of us can sit on the sidelines.”

She thanked her supporters, whom she called “my champions — my sisterhood of the traveling pantsuits. You never gave in. You never gave up. And together, we made history.”

Her speech gave the convention an emotional lift after a desultory second day of speeches by a parade of Democratic politicians.

Her uncompromising appeal for party unity behind Obama may have given the convention the spiritual lift it seemed to be lacking to that point, and put emotion behind a gathering that otherwise spent the day stressing that Obama's economic plan is starkly different from the Republicans'.

Clinton reaffirmed her support for Obama in soaring and unconditional language, and she betrayed none of the anger and disappointment that friends says she still feels and has especially haunted her husband.

Clinton urged Democrats to put aside their personal loyalty to her and unite behind Obama — or else risk continuing Bush administration policies under the presumptive Republican nominee, Sen. John McCain.

“You haven't worked so hard over the last 18 months, or endured the last eight years, to suffer through more failed leadership. No way, no how, no McCain,” she said.

Former Virginia Gov. Mark Warner, the convention's keynote speaker, tried to hammer home that message, warning that Republican rival John McCain “promises more of the same.”

Warner was received politely, but Clinton was clearly the evening's main event.

The party's unity remains fragile, and the delegates' mood is palpably tentative. That was obvious throughout the Pepsi Center, where scores of delegates wore their Hillary buttons and waved big white “H” signs. Those delegates were generally ready to accept Obama, but they really wanted Clinton.

“I've loved her for years,” said Carolyn Covington, a retired teacher from Palmer, Alaska. “But I'm going to be out there rooting for Obama.”

The quest for harmony continues today, when the featured prime-time speaker is former President Bill Clinton, who implicitly suggested Tuesday that Obama may be a weak candidate.

“Suppose you're a voter, and you've got candidate X and candidate Y. Candidate X agrees with you on everything, but you don't think that candidate can deliver on anything at all,” Clinton asked. “Candidate Y you agree with on about half the issues, but he can deliver.

“Which candidate are you going to vote for?”

The former president quickly added, “This has nothing to do with what's going on now.”

Hazel Rigby, a retired Alexandria, Va., teacher, knew who she'd vote for. “If we were to do 10 ballots, I'd support her on every one,” she said. “Unity is overrated.”

Delegates were confused about how a roll call of the states will proceed today.

The Clinton and Obama camps were discussing a deal in which some states would cast votes on the convention floor in prime time, then Clinton or a supporter would move to make the Obama nomination unanimous.

Clinton wasn't saying what she'd do, however, and some delegates indicated that they'd be upset if they couldn't vote for her.

Female delegates rallied during the day at the Colorado Convention Center, and when speakers mentioned Obama's name, they shook souvenir tambourines in unison. Few dissented.

The New York Times contributed.