Despite lingering unhappiness among some delegates nursing grievances over Clinton's loss, party chairman Howard Dean declared the convention determined to make Barack Obama the nation's first black president. "There is not a unity problem. If anyone doubts that, wait till you see Hillary Clinton's speech," he said.

Former Virginia Gov. Mark Warner was tapped to deliver the keynote address on the convention's second night. It was the same assignment that Obama - then an Illinois state lawmaker running for the Senate - used four years ago to launch his astonishing ascent in national politics.

Clinton paid an advance visit to the convention hall in late morning with her daughter, Chelsea. While her appearance was the main event of the night, it was far from the role she envisioned more than a year ago when she launched her bid to become the first female commander in chief. She was the prohibitive front-runner then, but soon found herself in a riveting struggle with Obama that she could not win.

Obama campaigned in Missouri Tuesday as he slowly made his way toward the convention city. Speaking to airline workers in a giant hangar, he accused the Bush administration of failing to enforce health and safety laws and said McCain "doesn't get it" when it comes to the concerns of blue collar workers.

The 47-year-old Illinois senator formally receives the nomination Wednesday in a roll call that will also give Clinton's supporters a chance to cast votes for her.

Obama delivers his acceptance speech Thursday night at a football stadium. An estimated 75,000 tickets have been distributed for the event, meant to stir comparisons with John F. Kennedy's appearance at the Los Angeles Coliseum in 1960.

The Republican National Convention meets in St. Paul, Minn. next week to nominate McCain and his still-unnamed running mate. That will set the stage for a final sprint to Election Day in a race that is remarkably close.

Obama's aides, already working to ease the ill feelings among Clinton's delegates, suddenly grappled with a second challenge when two well-known aides to former President Clinton said the convention speeches were too timid.

Paul Begala spoke dismissively of Warner's plans to go easy on McCain. "This isn't the Richmond Chamber of Commerce," he said.

"If this party has a message, it's done a hell of a job hiding it," James Carville told CNN as he reviewed the opening night's program.

If Obama's advisers had any reaction to the sniping, they kept it to themselves. The Illinois senator has cast himself as a different kind of politician, a "post-partisan" whose stock in trade is to forge a change in the way campaigns are conducted. Still, Obama has gone after Clinton and McCain sharply when aides thought it necessary.

"My inclination is you have to be careful about attacking McCain" because his life's story buys him deference, Tennessee Gov. Phil Bredesen said in an Associated Press interview. The Republican presidential hopeful was a prisoner of war in Vietnam for more than five years.

Dean, the party chairman, bristled at criticism from two of the men who helped put Bill Clinton in the White House.

"We don't need to attack McCain" at the convention's opening events, he said. "There will be plenty of time for that."

He added there are other imperatives for a week of convention speechmaking, principally, "to make sure people know who Barack Obama is, who Joe Biden is."

Biden, a Delaware senator, is Obama's vice presidential pick, already making the rounds of the convention city.

While Monday's opening convention session had a feel-good quality, with an emotional appearance by ailing Sen. Edward M. Kennedy and a prime-time speech by Michelle Obama. It seemed unlikely that would continue unabated, though, with second-night speeches by congressional leaders comfortable in the rough-and-tumble of political debate.

Whatever tone the Democrats took, there was no mistaking McCain's intentions.

For the second time in three days, his campaign sought to use Clinton to wound Obama. This time is was a television commercial that made use of a memorable ad she ran in the primaries.

It shows sleeping children and a 3 a.m. phone call into the White House portending a crisis. In the new ad Clinton is shown saying: "I know Sen. McCain has a lifetime of experience that he will bring to the White House. And, Sen. Obama has a speech he gave in 2002."

A narrator adds: "Hillary's right. John McCain for president."

Some Democrats expressed concern about the potential for at least the appearance of disunity on television later in the week.

Don Fowler, a former party chairman, said there was more of a problem than he had anticipated.

"All you need is 200 people in the crowd to boo and stuff like that and it will be replayed 900 times. And that's not what you want out of this."