John Bacon, and Richard Wolf

USA TODAY

PHILADELPHIA — The Democratic convention that will make Hillary Clinton the first woman ever nominated by a major party for president opened Monday with protests in support of the man she defeated, Bernie Sanders -- who received the night's lengthiest and most rousing reception.

Imitating the dissension that marked the Republican National Convention in Cleveland last week, disconsolate delegates supporting Sanders interrupted speakers with cries of "Bernie! Bernie! Bernie!" A few even chanted the GOP's mantra: "Lock her up!"

Their anger was prompted by an email scandal that revealed favoritism inside the Democratic National Committee for Clinton and forced party chairwoman Debbie Wasserman Schultz to relinquish the job. As a result, days after Republican nominee Donald Trump's controversy-laden Republican convention staggered to a finale, Democrats stumbled out of the box themselves.

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The protests subsided as the evening wore on, however, and the Democratic faithful were treated to unifying speeches from Sanders and others popular among the party's left wing: Sens. Elizabeth Warren and Cory Booker.

"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 "political revolution" will go on with his help -- and in the meantime, "any objective observer will conclude that – based on her ideas and her leadership – Hillary Clinton must become the next president of the United States." Delegates on both sides gave him a standing ovation -- with his supporters continuing to chant his name rather than Clinton's.

First lady Michelle Obama led the 10 p.m. prime-time hour with a passionate appeal on behalf of a former first lady "who has the guts and the grace to keep coming back and putting those cuts and those cracks in that highest glass ceiling.”

“Because of Hillary Clinton, my daughters and all of our sons and daughters now take for granted that a woman can be president of the United States," she said.

Speakers included all elements of the diverse party, displaying a different image than the Republicans' mostly-white mosaic: African Americans and Asian Americans, Latinos threatened by Donald Trump's desire to crack down on immigration, gays and lesbians, people with disabilities and mental illness. The most popular sign held aloft by delegates read, "Love trumps hate."

Speaker after speaker denounced Trump for his divisive rhetoric, interspersed with videos displaying some of the Republican nominee's most outrageous statements.

"That’s Donald Trump’s America: An America of fear and hate," Warren said. "An America where we all break apart. Whites against Blacks and Latinos. Christians against Muslims and Jews. Straight against gay. Everyone against immigrants. Race, religion, heritage, gender – the more factions, the better."

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Throughout the evening, other speakers sought to bridge the very real gap between Clinton's and Sanders' supporters by stressing their similarities -- such as on education, where Clinton has endorsed debt-free college at public universities. Sanders would go further.

"Bernie's ideas. Hillary's ideas. Our shared ideas," Booker said.

"We cannot be seduced by cynicism about our politics because cynicism is a refuge for cowards," the popular first-term New Jersey senator said. "We will not surrender the moral high ground.... In America, love always trumps hate."

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Comedian Sarah Silverman brought the house down by declaring her devotion to Sanders but her vote for Clinton, noting the prospective nominee had agreed to incorporate some of Sanders' goals into the party platform. "That is the process of democracy at its very best," she said. "Hillary is the Democratic nominee, and I will proudly vote for her."

Then, noting many delegates continued to shout "Bernie!" over and over, she added, "To the 'Bernie or bust' people, you're being ridiculous." At that point, Paul Simon came out to sing "Bridge Over Troubled Waters."

The stakes for the Democrat's convention are high: CNN and CBS polls released Monday indicated that, warts and all, the GOP convention may have provided enough bounce for Trump to inch ahead of Clinton.

The four-day homage to the nation's first female nominee for president took an early hit with the pre-convention release by Wikileaks of almost 20,000 Democratic Party emails, some of which showed Democratic staffers clearly favoring Clinton over Sanders in the midst of the hard-fought primaries. In one email, a DNC official suggests the party could damage Sanders in the South by pressing him on his religious beliefs. In another, Wasserman Schultz refers to Sanders’ campaign manager as a “damn liar.”

The FBI announced it was investigating a hack involving the emails. The New York Times reported that researchers at CrowdStrike, a California-based cybersecurity firm, linked the breach to Russian intelligence agencies. Crowdstrike declined a request for comment from USA TODAY.

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The Democratic National Committee issued a statement apologizing to Sanders, his supporters and the party for the "inexcusable remarks made over email," saying the comments "do not reflect the values of the DNC or our steadfast commitment to neutrality."

Sanders tried to tamp down the uprising among his supporters by sending an email warning that "our credibility as a movement will be damaged by booing, turning of backs, walking out or other similar displays. That's what the corporate media wants. That's what Donald Trump wants. But that's not what will expand the progressive movement in this country."

Sanders' speech at the end of the night was critical — and late in the day, convention leaders moved it to the end of the night to assure prime-time TV coverage. In a passionate warm-up appearance Monday afternoon before hundreds of his delegates, Sanders made it clear he would not lead a rebellion against Clinton.

"We have got to defeat Donald Trump," Sanders said to cheers -- before drawing jeers by adding, "and we have got to elect Hillary Clinton and Tim Kaine," her vice presidential running mate.

He won the crowd back by returning to Trump, their unifying force, much like Clinton was the only thing that united Republicans in Cleveland last week. "Trump is a bully and a demagogue," Sanders said. "Trump has made bigotry and hatred the cornerstone of his campaign."

Email has not been kind to Clinton, who survived an exhaustive investigation of her use of a private email server while secretary of State. Republicans howled foul, but the FBI declined to recommend criminal charges.

Clinton now must work to keep Democrats in line. Speaking in Charlotte, N.C., on Monday, she dismissed the Trump campaign as divisive and negative, accusing Trump of spending all his time "trash-talking the United States."

“We’re going to have a convention that highlights success stories," she said.

Despite Sanders' vigorous endorsement of Clinton, rumblings of dissent were everpresent. Texas delegate Barbara Fetonte, 63, expressed the frustration many Sanders supporters feel.

“We know Bernie would be a much stronger candidate against Trump," Fetonte said. "That’s also what’s making this so hard – she’s not a strong candidate.”

Clinton's fans sympathized with the Sanders crowd but predicted they would come around by the end of the four-day extravaganza.

"They’ve got a little bit of stuff they need to get out of them, and then they’ll be ready to get on board," said Patsy Keever, who chairs North Carolina's Democratic Party.

City officials had said they expected 50,000 protesters to flock to the city. Not nearly that many people had gathered by the first day. As of Monday afternoon, officials said sweltering heat approaching 100 degrees was their main concern.

Police Commissioner Richard Ross described the protests as "very peaceful" and said no arrests had been made.

Contributing: Michael Collins, Nicole Gaudiano, Susan Page, Eiza Collins and Paul Singer