Bernie Sanders loyalists heckled and hassled Democratic stars all day. But when Sanders himself addressed the Democratic National Convention on Monday, the party's nightmarish day finally brightened.

"Hillary Clinton must become the next president of the United States," Sanders boomed. And delegates, for the most part, cheered his call.


That was the clearest sign of an easing after an excruciating day of failed attempts at projecting unity following the divisive and protracted Democratic primary.

Sanders, at times, struggled to calm his most ardent supporters, as TV cameras highlighted delegates in tears as he urged them to support Clinton. "Not for sale," some delegates screamed. Sanders received the warmest applause of the night, basking in prolonged cheers as he took the stage, some of his delegates chanting "It's not over."

But Democrats ended the night more optimistic than they began it — when failed and frantic attempts by Clinton and Sanders aides to quiet rebellious pro-Sanders delegates plunged the convention into acrimony. Instead, a stirring speech by Michelle Obama, bookended by an uplifting — if high-decibel speech — by Sen. Cory Booker and liberal red-meat address from Sen. Elizabeth Warren seemed to get the convention back on track.

"This election and every election is about who will have the power to shape our children for the next four or eight years of their lives," Obama said, as a sea of "Michelle" placards waved in the foreground. "And I am here tonight because in this election, there is only one person who I trust with that responsibility, only one person who I believe is truly qualified to be president of the United States, and that is our friend, Hillary Clinton.”

Whether they can keep it there is an open question, as Sanders' diehard backers — even without the blessing of their candidate — plot to disrupt proceedings Tuesday, when Clinton is set to be formally nominated. The so-called Bernie Delegate Network, a group of Sanders' most vehement supporters, has flirted with the notion of challenging Clinton's vice presidential pick, Tim Kaine, though Sanders' campaign has disavowed those efforts. New protests erupted after the close of convention proceedings, a reminder that lingering bitterness could become a headache on the convention's second day.

It was precisely the outcome Clinton and Sanders aides had hoped to avoid. Convention organizers seemed intent on allowing Sanders' allies a catharsis, a chance to celebrate their candidate and even vent about their loss to Clinton during the convention's early hours, while speakers slowly began nudging them to line up behind Clinton as the day wore on.

Republicans gleefully latched onto that discord to try and wrest disgruntled Sanders supporters into the campaign of Donald Trump. Trump himself made an appeal to Sanders backers during his speech.

"Sad to watch Bernie Sanders abandon his revolution," he tweeted. "We welcome all voters who want to fix our rigged system and bring back our jobs."

Even as the convention seemed to shift toward unity later in the evening, bursts of discord broke through.

A small core of loud Clinton detractors chanted "black lives matter" while Booker spoke. A chorus of "we trusted you" jeers greeted Warren as she delivered a prime-time address. Some scattered pro-Sanders cries even broke through while Obama delivered the most well-received speech of the evening.

The tension broke through once again when comedian Sarah Silverman, a hard-core Sanders supporter, appeared alongside Sen. Al Franken and scolded the disruptive delegates. "To the Bernie or bust people, you’re being ridiculous," she said, as the crowd booed and broke into "Bernie" chants.

In the moments before the convention gaveled in, Clinton aide Marlon Marshall and Sanders deputy campaign manager Rich Pelletier huddled to discuss preventing visible disruptions by Sanders allies. Throughout the opening hours, Sanders campaign manager Jeff Weaver and senior strategist Mark Longabaugh, along with Marshall, Clinton campaign manager Robbie Mook and senior adviser Charlie Baker worked to soothe the discord, passing instructions to Sanders floor whip leader Robert Becker and Clinton's floor whip leader Donnie Fowler.

Sanders sent out a last-minute text message to his delegates encouraging them to “not engage in any kind of protest on the floor.”

“It’s of utmost importance you explain this to your delegations,” Sanders wrote in the text.

It was the first acknowledgment that an attempt to appease Sanders supporters earlier in the day — the ouster of outgoing DNC chairwoman Debbie Wasserman Schultz from the convention stage — had fallen short. Some Sanders allies, still fuming over leaked emails that showcase the DNC leadership’s favoritism for Clinton, chanted “lock her up” on the convention floor — echoing a Republican rallying cry from last week’s GOP national convention.

Ohio Rep. Marcia Fudge, who stepped in to chair the convention in place of Wasserman Schultz, found herself immediately drowned out by restive Democratic delegates screaming support for Sanders and wielding signs encourage the defeat of the Trans-Pacific Partnership.

"Excuse me," an irritated Fudge chided delegates from the podium. "I intend to be respectful of you, and I want you to be respectful of me. We're all Democrats and we need to act like it!"

Subsequent speakers were continuously interrupted by pro-Bernie chants — even as they pleaded for unity.

“Hillary Clinton and Bernie Sanders are our champions. They both deserve our cheers,” said Wellington Webb, former mayor of Denver.

The fractious opening note of the convention came as the DNC worked intensely to soothe Sanders allies.

"On behalf of everyone at the DNC, we want to offer a deep and sincere apology to Senator Sanders, his supporters, and the entire Democratic Party for the inexcusable remarks made over email,” the DNC said in a statement from its leadership. “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.”

Prominent Democratic elected officials pleaded with their states' delegations to unify throughout the day.

Missouri Sen. Claire McCaskill, whose delegation was divided between Sanders and Clinton supporters, said her call for healing seemed to succeed.

"Some of them were a little stony-faced. Others nodded their heads. What I was trying to do was show them the respect they deserve," she said, adding, "Put yourself in their shoes. Many of them have never been involved in an organized political effort like this," she said. "The notion that anyone would expect them to come here and not cheer and not be heard. How silly is that?"

West Virginia Sen. Joe Manchin intends to speak to his state's Sanders-supporting delegates Tuesday morning.

"God bless 'em," Manchin said in an interview. "My only problem with Bernie is his solutions. He didn't have solutions."

"I'm hoping that they'll come around. We'll find out tomorrow," he added. "I mean it doesn't make any sense. Where are they gonna go?"

The mayhem mirrored a similar clash on the floor of last week’s Republican National Convention, where conservative delegates and opponents of Donald Trump attempted to force an uncomfortable vote on a package of party rules that would have highlighted the GOP’s lingering disunity. But that rebellion was quickly stamped out by Republican National Committee leaders and pro-Trump convention whips. RNC Chairman Reince Priebus was quick to highlight the divisions among Democrats.

“Feels more like @BernieSanders’ convention than @HillaryClinton’s,” tweeted RNC Chairman Reince Priebus.

Trouble started early Monday, when Wasserman Schultz's debut at the convention proved disastrous. The Florida congresswoman as was heckled as she tried to speak before the Florida delegation breakfast, with some in the room yelling "Shame!"

"So I can see that's little bit of interest in my being here and I appreciate that interest," Wasserman Schultz said amid the cacophony. "And a little bit of interest from the press but that really shows you that Florida is the most significant battleground state that will make sure that Hillary Clinton is elected president of the United States of America. We are the state that will deliver the White House to make sure that we can continue to make the progress that we have been able to make under Barack Obama for the last eight years."

By Monday afternoon, as concerns grew about Wasserman Schultz also being jeered on stage, the outgoing DNC chair said she would step aside.

"I have decided that in the interest of making sure that we can start the Democratic convention on a high note that I am not going to gavel in the convention," Wasserman Schultz told the Sun Sentinel.

Sanders himself provoked outrage from his supporters on Monday after he declared that the time has come for them to elect Clinton and vice presidential nominee Tim Kaine.

"Immediately right now, we have got to defeat Donald Trump. And we have got to elect Hillary Clinton and Tim Kaine," Sanders said at the Philadelphia rally, drawing boos and subsequent chants of "we want Bernie."

By early afternoon, Sanders allies were openly discussing plans to challenge Clinton's selection of Tim Kaine as her running mate.

“There’s serious interest right now and exploration as we speak of a formal challenge,” Norman Solomon, a California delegate and national coordinator for the Bernie Delegates Network, said at a news conference Monday. A formal challenge would feed Republican glee over the Democrats' rocky first day. Though restive delegates at last week's Republican National Convention had chattered about trying to hijack Trump's vice presidential selection, no formal effort materialized.

Weaver, Sanders' campaign manager, disavowed the effort, telling reporters that the push would be "divisive."

Burgess Everett, Shane Goldmacher, Julia Ioffe, Gabe DeBenedetti, Nolan McCaskill and Nick Gass contributed to this report.