Democrats opened their national convention Monday amid the clamor of jeers and catcalls, as supporters of Vermont Sen. Bernie Sanders booed the mere mention of Hillary Clinton and assailed party leaders for the favoritism they showed in her fight for the party nomination.

For a second day, a series of leaked emails revealing the party’s pro-Clinton tilt overshadowed efforts to rally delegates behind the presumptive nominee and end her campaign fight with Sanders on a harmonious note.

Live updates from the Democratic National Convention in Philadelphia »

Convention planners assembled a prime-time lineup that included First Lady Michelle Obama, a keynote address by Massachusetts Sen. Elizabeth Warren — a favorite of the populist left — and a supportive speech by Sanders under the umbrella of a “United Together” theme.

But the notion of unity was more aspirational than real.

The leaked emails cost Democratic National Committee Chairwoman Debbie Wasserman Schultz her job, effective once the convention ended, and led some Sanders supporters to redouble their efforts to deny Clinton the nomination or, at the least, use a roll-call vote to put their dissent on full, enumerated display.

Even Sanders was unable to appease his restive backers.

As he addressed a crowd of supporters before his prime-time appearance, the cheers that greeted his call to defeat Republican nominee Donald Trump — “a bully and a demagogue”— immediately turned to boos when he urged the election of Clinton.

The loud dissent spilled over to the formal proceedings the moment the convention began, starting with the opening prayer and continuing intermittently throughout the night.

“We are all Democrats,” Rep. Marcia L. Fudge of Ohio, who wielded the convention gavel, chided at one point. “We need to act like it.”

But the dissenters were undeterred — even after the Democratic National Committee issued a formal apology and Sanders sent an admonishing email telling his delegates the credibility of his campaign and the causes he espoused would be undermined by such outbursts.

From the California section of the convention floor came a chant of “Lock her up” — the derisive call that became an anti-Clinton rallying cry at last week’s Republican convention.

Amid the dissent, Trump was hardly ignored. One speaker after another assailed him as a plutocrat trying to fool working families into believing he’s on their side.

"Donald Trump, you're no tough guy,” bellowed AFL-CIO President Richard Trumka. “You're a phony!”

Clinton’s campaign had promised a precision-driven gathering that would contrast with the upheaval at the GOP convention, with its blunders over scheduling, a plagiarized speech by Trump’s wife, Melania, and the booing of Texas Sen. Ted Cruz when he refused to endorse Trump.

Their hopes quickly fizzled, in large part because — unlike Cleveland, which was boycotted by a number of leading Republicans — dissenting Democrats did not stay away from Philadelphia.

And though the party’s actions were hardly determinative in the nominating contest — Clinton won millions more votes — the partiality confirmed what Sanders and his supporters had long claimed — and deepened their hostility.

The day got off to a surly start when Wasserman Schultz was booed and heckled with cries of “shame” at a breakfast of her home-state Florida delegation.

The congresswoman from the Miami area was quickly shouted down as she began speaking of an overnight shooting at a Fort Myers, Fla., nightclub. “People lost their lives," she began before being drowned out.

When Florida’s party chairwoman, Allison Tant, sought to intervene, someone shouted out, "We didn't have our voice!,” alluding to suggestions the nominating fight was rigged in Clinton’s favor.

Wasserman Schultz briefly carried on before giving up and leaving under a security escort; in a further slap, she was stripped of the traditional honor of wielding the gavel to open and close the convention.

Several lawmakers, including House Democratic Leader Nancy Pelosi, received a similarly rowdy reception when they spoke at California’s delegation breakfast. Sanders supporters waved "Bernie or Bust" signs and chanted the senator’s name whenever a speaker mentioned the presumptive party nominee.

Pelosi responded evenly, with a gentle reproach.

“People get excited about the campaigns that they are in, and it doesn't turn off the day the determination is made," the San Francisco lawmaker said, suggesting a time comes to move on. "Some people are new and just are not familiar with how things work. "

As Sanders' delegates tried to decide how much — and how visibly — to protest, California’s biggest-in-the-nation delegation took a lead role in the informal deliberations. With about 200 Sanders backers, Californians made up more than a tenth of his support in Philadelphia.

"We have everything from the ‘Bernie or Busters’ to what I call the eventual-nominee types," said Karen Bernal of Sacramento, the co-leader of the Sanders California delegation.

Though party leaders want the focus to be unity, "Bernie delegates came here with an entirely different agenda," Bernal said, speaking at a news conference called by a group of Sanders supporters. "We came here to push a progressive agenda."

Clinton, meantime, sought to focus attention on her policy agenda in a speech to veterans in Charlotte, N.C.

“I am not a newcomer to these issues,” she said at the Veterans of Foreign Wars gathering, drawing an implicit contrast to Trump. “I believe the United States of America is an exceptional nation with capabilities that no other nation comes close to matching. We have the world’s greatest military. Don’t let anyone tell you otherwise.

“I’m not interested in talking provocatively,” Clinton said. “I’m not interested in insulting people, including our military. I’m interested in bringing our country together. I’m interested in healing the divisions.”