The Democratic National Convention got off to a rocky start Sunday even before the first gavel fell.

Amid a controversy over emails showing that national party operatives were scheming to undermine Bernie Sanders during the presidential primary campaign, the embattled Democratic national chairwoman, Debbie Wasserman Schultz, announced on Sunday that she would quit after the convention.

She already had been stripped of her position as chair of the convention after facing intense criticism that she and her operation were biased in favor of Hillary Clinton during the primary.

Wasserman Schultz had faced growing pressure, including from Sanders, to step aside. On the eve of a convention meant to show party unity here in Philadelphia, the controversy threatened to inflame Sanders supporters, who have long believed that he was treated unfairly, and thousands of whom flooded Philadelphia streets Sunday.

Her resignation came as Sanders was preparing for a Monday speech in which he was expected to urge his loyalists to rally behind Clinton, a task now made more difficult by leaked e-mails showing supposedly neutral national Democrats discussing ways to undercut Sanders, including by questioning his religion.

It also comes after days of Democratic crowing over GOP missteps and divisions at the Republican convention in Cleveland last week.

Wasserman Schultz had sarcastically tweeted at her GOP counterpart, Reince Priebus: "Hey @Reince - I'm in Cleveland if you need another chair to help keep your convention in order."

On Sunday she said that electing Clinton "is critical for America's future" and that she would continue to work as a surrogate for the Democratic nominee.

"Going forward, the best way for me to accomplish those goals is to step down as party chair at the end of this convention," said the statement from Wasserman Schultz, a member of the U.S. House of Representatives from Florida.

Donna Brazile, a longtime Democratic strategist who has a high profile from numerous TV appearances, will take over temporarily as party chair.

Former Gov. Ed Rendell, who also once chaired the Democratic National Committee, said the party has an obligation to stay neutral in primaries. When he led the party in 1999, he said, he wrote a $1,000 check to the campaign of then-presidential contender Bill Bradley - to match the $1,000 Rendell had already donated to Al Gore's run.

"They violated that basic rule," Rendell said Sunday. "And whether Debbie had anything directly to do with it or not, and it appears from some of the emails she was somewhat involved, she certainly has responsibility for this."

Rendell, who, like Sanders, is Jewish but non-practicing, called the leaked e-mails about Sanders' lack of overt religiousness "unconscionable."

"I would have been highly offended if someone said something like that about me. We all chose to worship God in our own way," Rendell said. "I think [Sanders] has the right to be highly offended."

The flap could fuel the ire of many Sanders supporters who remain skeptical about Clinton. It also adds importance to the keynote address that Sanders is scheduled to deliver Monday night at the Wells Fargo Center.

"It makes Sanders' job that much harder tomorrow night in convincing his followers," said Patrick Murray, a pollster at Monmouth University. "He can still give a strong endorsement of Hillary Clinton, but he can't give a strong endorsement of the process."

Sanders and his backers have long accused Wasserman Schultz's DNC of putting its thumb on the scale to help Clinton win the nomination.

On Sunday, Sanders called for Wasserman Schultz to resign. After she did, he said she made the right decision for the future of the Democratic Party.

"While she deserves thanks for her years of service, the party now needs new leadership that will open the doors of the party and welcome in working people and young people," the Vermont senator said in a news release. "The party leadership must also always remain impartial in the presidential nominating process, something which did not occur in the 2016 race."

Priebus, here Sunday to open the party's rapid-response operation, said the controversy showed Democratic disarray.

"When you rig a system and spread emails around to senior staff in that manner, I think this kind of outcome is inevitable," said Priebus, who was joined by Paul Manafort, GOP nominee Donald Trump's campaign manager. "The other thing is, you don't say stupid stuff in emails and send it around."

Earlier Sunday, Clinton campaign chief Robby Mook suggested Russians were behind the hacking of DNC emails in order to help Trump, an unabashed admirer of Vladimir Putin. Manafort brushed that off, saying Democrats were "pretty desperate pretty quickly."

Clinton said in a statement that she was grateful to Wasserman Schultz for her work and that "this week's events will be a success thanks to her hard work and leadership."

Wasserman Schultz said her resignation would take effect after the convention. Party officials said she would gavel the gathering to order Monday and close it on Thursday, but would have no major speaking role - unlike Priebus at the GOP convention last week.

Instead, U.S. Rep. Marcia L. Fudge (D., Ohio) will lead the proceedings.

Wasserman Schultz's Monday morning address to Pennsylvania's delegates was canceled as well.

The controversy emerged from a trove of 20,000 emails of top DNC officials released Friday by Wikileaks. Some of them showed party staffers suggesting an attack on Sanders based on his religious beliefs, and a plan to scuttle a previously agreed-to debate before the June 3 California primary because that was what Clinton's team wanted.

While Sanders identifies as Jewish, he is not overtly religious. One email suggested using the Vermont senator's beliefs to hurt him with voters in Kentucky and West Virginia.

"It might may no difference, but for KY and WVA can we get someone to ask his belief," Brad Marshall, chief financial officer of the national committee wrote May 5. "Does he believe in God. He had skated on saying he has a Jewish heritage. I read he is an atheist. This could make several points difference with my peeps. My southern baptist peeps would draw a big difference between a Jew and an atheist."

Amy Dacey, chief executive of the DNC, later replied "AMEN," according to the leaked emails.

Murray, the pollster, said the e-mails reinforce the long-running belief of some critics that Clinton and her supporters will do almost anything to win.

Rendell, a Clinton booster, said he hoped Wasserman Schultz's resignation would help calm the anger from Sanders supporters.

"There's been harm done but there's plenty of time to undo that harm," he said.

U.S. Rep. Brendan Boyle (D., Pa.), called Wasserman Schultz's decision gracious and said she "put party unity first."

tfitzgerald@phillynews.com

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@tomfitzgerald

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Staff writer Tricia Nadolny contributed to this article.