Democrats opened their national convention in Philadelphia on Monday with a tightly scripted message of party unity, even as they angled to tamp down internal discord that threatened to overshadow the event.

A roster of bold-faced and little-known party names implored supporters to unite behind Hillary Clinton and put aside the acrimony suddenly reignited by the email scandal that showed leaders plotted through the primary to beat back Sen. Bernie Sanders' campaign.

As her delegates started to gather in South Philadelphia, thousands of his fervent loyalists filled the sweltering city streets to protest what they called indefensible bias by the party establishment. Dozens were briefly detained when they tried to storm barricades outside the Wells Fargo Center.

Inside, Sanders himself tried to quell the discontent. Handed the keynote speaking slot, the Vermont senator told delegates and supporters that despite their disagreement on some issues, he was solidly behind the nominee.

"Based on her ideas and her leadership, Hillary Clinton must become the next president of the United States," Sanders said. "The choice is not even close."

His words came against a stormy backdrop of growing discontent that suggested Democrats might struggle to portray their convention as the unified, forward-thinking antidote to last week's unpredictable gathering of Republicans in Cleveland.

Hours before the opening gavel, the fallout from last week's leaked emails continued. Already having pledged to resign over her ties to the messages, Democratic National Committee Chair Debbie Wasserman Schultz was forced to forgo any role at the convention.

DNC officials issued an apology for what they called the "inexcusable remarks" in the emails. "These comments do not reflect the values of the DNC or our steadfast commitment to neutrality during the nominating process," the party leadership said.

On the convention stage, speaker after speaker tried to steer the conversation to Clinton's strengths and her looming battle with Donald Trump. Unlike the GOP nominee, who made news and appearances on each day of his party's convention, Clinton remained out of sight, letting others campaign for her.

Michelle Obama heaped praise on her as a tireless public servant who has earned the job and who will never quit. "Because of Hillary Clinton, my daughters, and all our sons and daughters, now take for granted that a woman can be president of the United States," Obama said.

Massachusetts Sen. Elizabeth Warren savaged Trump as a failed businessman without a plan, "a man who must never be president of the United States."

When speakers were not openly criticizing Trump, convention organizers turned down the lights and aired videos of the billionaire's most outrageous statements, and speakers urged the party faithful to stand together.

"When we are indivisible, we are invincible," New Jersey Sen. Cory Booker said.

Still, the division did not easily melt away. When, early in the proceedings, convention chair Marcia Fudge told the crowd she was excited to send "Hillary Clinton and Tim Kaine to the White House," loud boos floated up along with the cheers.

During remarks designed to persuade other loyal Sanders supporters to follow her lead and get behind Clinton, comedian Sarah Silverman - herself a Sanders supporter in the primaries, ad-libbed: "Can I just say to the Bernie-or-bust people, you're being ridiculous."

Instead of pacifying them, her comment stoked a new round of "Bernie! Bernie!" chants.

The chants resumed when Sanders took to the stage late Monday, drawing a sustained standing ovation. The packed Wells Fargo Center roared for minutes before letting him speak, holding pro-Sanders signs and others that read "Stronger Together" and "She's With Us." Some held back tears as he spoke.

Sanders thanked his supporters - 1,894 delegates, 46 percent of the total - saying he looked forward "to your votes during the roll call on Tuesday night."

But he also left no doubt that he supported the nominee.

"It is no secret that Hillary Clinton and I disagree on a number of issues," he said. "That's what this campaign has been about. That's what democracy is about. But I am happy to tell you that . . . there was a significant coming together between the two campaigns and we produced, by far, the most progressive platform in the history of the Democratic Party."

Sanders told the roaring crowd that the revolution to revive the middle class and uplift working families will continue.

Clinton, he said, understands the need to create jobs, pay a higher minimum wage, and battle the damaging effects of climate change. She wants to ensure universal access to health care and tackle immigration reform, he said, making her "the clear choice" in November.

"Hillary Clinton will make an outstanding president, and I am proud to stand with her here tonight," he said.

Political pollster G. Terry Madonna called Monday's events a pivotal moment for the party, but one that need not define the week's gathering. "What we don't know for sure is whether this is a moment or a movement," he said.

It was also unclear whether that discord would continue through the week. Earlier in the day, Sanders had urged his delegates to remain respectful at the convention.

"I ask you as a personal courtesy to me to not engage in any kind of protest on the floor," Sanders wrote in a text message blasted to delegates, including Gwen Snyder, a Philadelphia-based grassroots activist, after meeting with them.

As that meeting ended, some delegates remained resolute in their support of him. Some warned they may protest on the floor of the convention during Clinton's speech Thursday.

Corey Jones, a 19-year-old Sanders delegate from Anamosa, Iowa, said he was not satisfied with the apology to Sanders and his supporters.

"It's like a criminal apologizing for a crime but not being indicted for it," Jones said.

He plans to vote for Clinton, "but I'm going to fight until the end of the convention."

Denise Hartle, who drove from California for the convention activities, also said she hasn't given up hope for Sanders.

"There's always a sliver of hope," she said. "It's not over till it's over."

acouloumbis@phillynews.com717-787-5934@AngelasInk

Staff writers Jonathan Tamari and Julia Terruso contributed to this article.

Convention Schedule

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For a complete schedule of today's events, including speakers and protests, go to philly.com/dnc EndText