Nicole Gaudiano

USA TODAY

WASHINGTON — Democrats hope to project an image of unity Monday as Bernie Sanders delivers opening remarks at the party's national convention. But an email scandal and the subsequent resignation of the national party's top official threaten to undermine that theme.

The Vermont senator said Sunday he wasn’t shocked but was “disappointed” by Democratic National Committee emails that suggest DNC officials were hostile toward his presidential campaign and favored former secretary of State Hillary Clinton. In one email among the thousands released by Wikileaks, a DNC official suggests the party could use questions about Sanders’ faith to hurt him in the South. In another email, the DNC's chairwoman, Rep. Debbie Wasserman Schultz of Florida, refers to Sanders’ campaign manager as a “damn liar.”

On Sunday, Wasserman Schultz said she will step down as DNC chairwoman at the conclusion of this week's convention in Philadelphia. But she also said she plans to open and close the convention and to "address our delegates about the stakes involved in this election not only for Democrats, but for all Americans."

Amid email uproar, Wasserman Schultz to step down after convention

Clinton’s convention to go straight at trust issue

Sanders issued a statement Sunday saying Wasserman Schultz "has 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," Sanders said. "The party leadership must also always remain impartial in the presidential nominating process, something which did not occur in the 2016 race."

In appearances on talk shows earlier Sunday, Sanders had again called for Wasserman Schultz’s resignation but said Democrats should focus on defeating GOP nominee Donald Trump, whom he called “perhaps the worst Republican candidate that I’ve seen in my lifetime.”

“We have to elect Secretary Clinton, who on every single issue — fighting for the middle class, on health care, on climate change — is a far, far superior candidate to Trump,” Sanders said on Meet the Press. “That’s where I think the focus has got to be.”

DNC emails show hostility to Sanders; one calls campaign chief 'damn liar'

Sanders’ will hammer that point home in his speech Monday and will "rip into Trump” for denying climate change is real, according to his campaign. He also will note the “most progressive platform in Democratic Party history” includes agreements he reached with Clinton to expand access to health care and make public college tuition-free for students from families with annual incomes up to $125,000 a year.

Sanders also will tell the 13 million voters who supported him during the primary season that the political revolution they helped him launch continues, according to the campaign.

“Together, we continue the fight to create a government which represents all of us, and not just the 1%," he will say, according to the campaign. "A government based on the principles of economic, social, racial and environmental justice.”

Unlike Sen. Ted Cruz of Texas, who shocked the GOP's national convention in Cleveland last week by not endorsing Trump during his speech, Sanders endorsed Clinton at a New Hampshire rally on July 12 and said he will do everything he can to help her defeat Trump.

“Will I be very active in this campaign? The answer is, I will, and that will start after the convention,” he told USA TODAY on July 14.

Sanders will address the Democratic convention the same night that first lady Michelle Obama and immigration activist Astrid Silva will speak. Convention officials said the night's “United Together” theme will focus on building an economy that works for everyone, “not just those at the top” — one of the mantras of Sanders’ campaign.

Outside the convention, thousands of Sanders’ supporters are expected to protest party leadership and call for reforms.

'Bernie or Bust' backers to flock to Philly to protest

The DNC emails released by Wikileaks are bound to fuel their sense that national Democratic officials betrayed Sanders. The emails also will make it more difficult for Sanders to rally his supporters behind Clinton because they likely will believe she was in “collusion” with the DNC, said Patrick Murray, director of the Monmouth University Polling Institute.

“The wound hasn’t healed yet," he said. "It’s ripping off the scab and reopening it. In the end, they’re going to vote for her. The impact is on the level of enthusiasm. What (Democrats) were hoping for is a clean convention with Sanders sending a very clear signal with his speech that ‘We’re all united behind Clinton.’ These email leaks just make it harder for some of his supporters to do that in a very enthusiastic way.”

Tensions already were high between Sanders and the DNC. Earlier in the campaign, they feuded over the Democratic debate schedule, access to a DNC voter database, a joint fundraising agreement between the DNC and Clinton, and representation on convention committees.

“It confirms what was evident for months — the heavy-handed role of the DNC to predetermine the outcome of the primaries and their one-sided collaboration with the Clinton campaign (and, apparently, a few people in the media),” emailed Charles Idelson, spokesman for National Nurses United, which supported Sanders’ campaign.

Sanders, who has raised money for Wasserman Schultz's primary opponent, has frequently said the party needs a new leader who will work vigorously to bring new people — especially working people and younger people, whom Sanders attracted in large numbers — into the political process.

Clinton campaign manager Robby Mook, speaking on This Week Sunday, noted that the DNC official who questioned Sanders’ faith has apologized, which he called “an appropriate step.” He said the DNC needs to look into the matter, take appropriate action and determine the accuracy of the leaks. Mook said the DNC account apparently was hacked by Russians to benefit Trump.

After news of the emails broke, Trump tweeted that “it will make it impossible for (Sanders) to support (Clinton), unless he is a fraud!” He followed up on Sunday with a tweet calling Sanders “exhausted” and saying it’s “sad” that he is “trying to dismiss the new e-mails and DNC disrespect.”

Trump tries to use Kaine pick to attract Sanders backers

Recent polls show most Sanders supporters are ready to back Clinton over Trump. A Pew Research Center survey, conducted June 15-26, found that 85% of Democrats and Democratic-leaning voters who backed Sanders in the primary said they plan to vote for Clinton in the general election. Nine percent said they'll vote for Trump and 6% said they'll vote for another candidate or don’t know.

Follow @ngaudiano on Twitter.