Philadelphia (CNN) Bernie Sanders on Monday and Tuesday led an orchestrated attempt by Democratic leaders to pull their party together, but simmering anger among his die-hard supporters proved that Democratic unity will be a work in progress.

On a dramatic first night of the Democratic convention, Michelle Obama brought the house down with an emphatic endorsement of Hillary Clinton. The first lady said she was the person most qualified to be president, and "I'm with her."

Other Democratic headliners, including Sens. Cory Booker and Elizabeth Warren, sought to make the case to Sanders supporters that a Donald Trump presidency would be so dire that they must vote for Clinton.

The most important political moment of the night came when Sanders delivered the full-throated endorsement that the Clinton campaign had longed for.

"Any objective observer will conclude that -- based on her ideas and her leadership -- Hillary Clinton must become the next president of the United States," Sanders told delegates, spurring a cascade of cheers.

He spent the following morning meeting with individual state delegations to carry his message forward and continuing to counter resistance toward Clinton.

Sanders chastened California delegates who booed his call for party unity Tuesday.

"Our job is to do two things -- to defeat Donald Trump and to elect Hillary Clinton," Sanders said, adding later, "It is easy to boo, but it is harder to look your kids in the face if we are living under a Trump presidency."

After a hard fought primary, he left no doubt about his position on the cusp of the general election.

Anger and loss

But all day long, there were signs that many Sanders supporters were still experiencing feelings of anger and loss at the effective end of his "political revolution." Their fury was exacerbated by a leak of Democratic National Committee documents that showed party leaders discussing how to thwart him during the primary.

And even on the convention floor, signs of discord were everywhere. One Clinton supporter, for example, got embroiled in an argument with a woman supporting Sanders, who had blue tape over her mouth reading "Silenced by the DNC."

Another Sanders delegate wearing a Marine Corps cap took a swing at a Clinton delegate before Secret Service officers broke up the fracas.

Comedian Sarah Silverman chastised booing Sanders fans during her remarks Monday.

"To the 'Bernie or bust' people, you're being ridiculous," Silverman said.

Some delegates had tears in their eyes as Sanders signaled that he felt the pain of those who had committed everything to his upstart political movement that at one point threatened to upend Clinton and the Democratic establishment.

"I understand that many people here in this convention hall and around the country are disappointed about the final results of the nominating process," Sanders said. "I think it's fair to say that no one is more disappointed than I am."

But he said his supporters had no choice but to swallow their dismay and take part in the election, given the alternative.

"If you don't believe this election is important, if you think you can sit it out, take a moment to think about the Supreme Court justices that Donald Trump would nominate and what that would mean to civil liberties, equal rights and the future of our country," he said.

Speaking at a Bloomberg Politics breakfast the morning after, Sanders expressed confidence that the "overwhelming majority" of his supporters will support Clinton in the fall.

"If you look at one issue after the other issue in terms of who the candidate is that we need to lead this country, there is no debate," Sanders said. "The choice in this campaign is very, very clear and I think the overwhelming majority of my supporters will see it that way."

The Vermont senator said after the election, he plans to use his increased "clout" after the election to make certain that his progressive ideas have life in Congress.

On what his message is going into Tuesday's roll call, Sanders said: "Vote for me." He went on to add that when his supporters return home, they should stay involved in the political process and work to make sure that Clinton elected president.

Michelle Obama

The star of the night was Obama, who delivered an unequivocal endorsement of Clinton and took a sharp swipe at Republican nominee Trump, sparking a euphoric reception.

"Don't let anyone tell you that this country isn't great. This right now is the greatest country on earth," the first lady said, slamming Trump as unfit for the presidency.

She added that being commander-in-chief was a job that could not be "boiled down to 140 characters."

Warren slammed Trump as a man who skipped on his debts and cheated other people, while saying Clinton was one of the "smartest, toughest most tenacious people on this planet."

Sanders spent much of Monday making a last-ditch effort to quell the anger among his backers, including texting supporters asking them not to "engage in any kind of protest on the floor. The appeal came after Sanders deputy campaign manager Rich Pelletier and Clinton aide Marlon Marshall met in a bid to head off any floor protests that would shatter the image of Democratic unity as the convention opened, a party official said.The frantic attempts to cool tempers came as DNC Chairwoman Debbie Wasserman Shultz was forced to resign on the eve of the convention in the wake of the email controversy. But the tension was slow to dissipate.

Rep. Elijah Cummings, D-Maryland, was drowned out in the afternoon by chants of "Stop TPP" — a reference to the vast trans Pacific trade pact that Sanders opposes and that Clinton backed while secretary of state. She has since come out against the deal.

As one speaker was imploring party unity from the dais, Kim Netherton, 31, a Sanders delegate from Colorado yelled out "Bulls--t!"

Chants of "We want Bernie!" and "Not for sale!" rang out as Maine State Rep. Diane Russell, a Sanders supporter, said their revolution must continue.

'We will always have a voice'

But as Russell implored the Sanders delegates, saying "We will always have a voice in the Clinton administration," Netherton and other Sanders delegates booed and yelled "Nooo!"

The woman with blue tape over her mouth, Diane Fowler, is a delegate from Michigan. She said would not fall in line — despite the unity effort by Democratic leaders "with what's coming out: the lying, the sabotage of Sanders campaign, and questions about the integrity of the voting."

Hoping to take advantage of the chaos, Republican Trump tweeted: "While Bernie has totally given up on his fight for the people, we welcome all voters who want a better future for our workers."

At an evening rally in Winston-Salem, North Carolina, Trump said Sanders is "losing his legacy."

"He's just sort of given up," Trump said.

The DNC is facing questions about whether it could have done more to limit the damage done by hackers suspected of working for Russian intelligence. Federal investigators tried to warn the DNC about a potential intrusion in their computer network months before the party moved to try to fix the problem, US officials briefed on the probe tell CNN.

The DNC issued an apology to Sanders moments after the convention opened Monday, likely hoping to soothe tensions heading into the week.

"On behalf of everyone at the DNC, we want to offer a deep and sincere apology to Sen. Sanders, his supporters, and the entire Democratic Party for the inexcusable remarks made over email," the statement said. "These comments do not reflect the values of the DNC or our steadfast commitment to neutrality during the nominating process. The DNC does not -- and will not -- tolerate disrespectful language exhibited toward our candidates. Individual staffers have also rightfully apologized for their comments, and the DNC is taking appropriate action to ensure it never happens again."