JONATHAN MARTIN and ALAN RAPPEPORT
Maggie Haberman, Trip Gabriel and Yamiche Alcindor contributed reporting.

Democrats arrived at their nominating convention on Sunday under a cloud of discord as Debbie Wasserman Schultz, the chairwoman of the Democratic National Committee, abruptly said she was resigning after a trove of leaked emails showed party officials conspiring to sabotage the campaign of Sen. Bernie Sanders, I-Vt.

The revelation, along with sizable pro-Sanders protests in the streets to greet arriving delegates in Philadelphia, threatened to undermine the delicate healing process that followed the contentious fight between Sanders and Hillary Clinton. And they raised the prospect that a convention that was intended to showcase the Democratic Party’s optimism and unity, in contrast to the Republicans, could be marred by dissension and disorder.

The day also veered extraordinarily into allegations, not easily dismissed, that Russia had a hand in the leaks that helped bring down the head of a U.S. political party.

Despite those concerns, Democrats are hoping that focusing on Donald Trump, the Republican nominee, will galvanize the party to rally around Clinton, and on Sunday those efforts received a major boost when Michael Bloomberg, the former Republican and independent mayor of New York, said he would endorse her.

In her resignation statement, Wasserman Schultz, a representative from Florida, said she would continue to fight for Clinton from the sidelines.

“I know that electing Hillary Clinton as our next president is critical for America’s future,” Wasserman Schultz said in a statement. “I look forward to serving as a surrogate for her campaign in Florida and across the country to ensure her victory.”

She added: “Going forward, the best way for me to accomplish those goals is to step down as party chair at the end of this convention.”

Donna Brazile, a vice chairwoman of the Democratic National Committee, will be the interim chairwoman through the election, the committee said.

Wasserman Schultz has faced a flurry of negative stories during her five-year tenure as the committee’s chairwoman, with critics charging that she was more focused on promoting her career than on the party, but she had resisted calls for her to quit.

Wasserman Schultz announced her resignation after a private meeting with advisers and senior aides to Clinton at a hotel here a day before the party’s convention was set to begin. She had faced growing calls for her resignation over the weekend.

“In politics, you need to not only know when to draw your sword, but also when to fall on it,” said James Carville, a longtime friend and adviser to the Clintons.

The breach of the Democratic committee’s emails, made public on Friday by WikiLeaks, offered undeniable evidence of what Sanders’ supporters had complained about for much of the senator’s contentious primary contest with Clinton: that the party was effectively an arm of Clinton’s campaign. The messages showed members of the committee’s communications team musing about pushing the narrative that the Sanders campaign was inept and trying to raise questions publicly about whether he was an atheist.

Sanders said the situation was an “outrage” on Sunday before the resignation was announced, and called for Wasserman Schultz to step down. Afterward, he said it was the right decision.

“The party leadership must also always remain impartial in the presidential nominating process, something which did not occur in the 2016 race,” he said in a statement.

Clinton’s campaign aides ignored questions as they quickly left a hotel a few minutes after the resignation was announced. Brazile emerged soon after the Clinton aides had left and said in a brief interview that Wasserman Schultz had called her Sunday afternoon and asked her to come to the hotel where the Florida delegation was staying.

Convention organizers had expressed nervousness on Sunday about the specter of Wasserman Schultz appearing on stage at all during the four-day convention. They were worried that what they intended to be a well-choreographed event, which officials hoped would contrast with the sometimes chaotic Republican National Convention, could be marred by Sanders’ backers booing and heckling her.

Wasserman Schultz recognized the magnitude of the problem on Saturday and initially planned to offer an apology, one of her advisers said. But it became clear to her on Sunday that contrition was insufficient.

Clinton’s campaign handled the situation delicately, not wanting the chairwoman to feel intense pressure and dig in. The Clinton aides told Wasserman Schultz the choice to resign was hers to make, but they gently warned her that she would face jeers from Sanders’ supporters in the convention hall this week, said the adviser to Wasserman Schultz, who requested anonymity to discuss private deliberations.

The nudge was enough to force Wasserman Schultz’s hand.

© 2016 New York Times News Service