PHILADELPHIA — First lady Michelle Obama stepped into the presidential election Monday with a forceful, impassioned defense of Hillary Clinton, casting her as the only candidate who can be trusted as a role model for the nation’s children. She took numerous swipes at Republican Donald Trump, all without mentioning his name.

“I want someone with the proven strength to persevere, someone who knows this job and takes it seriously, someone who understands the issues a president faces are not black and white,” Mrs. Obama said on the opening night of the Democratic convention. Referring to Trump’s penchant for tweeting, she said of the presidency: “It cannot be boiled down to 140 characters.”

The first lady was among a high-wattage line-up of speakers taking the stage, all but wiping away earlier tumult that had exposed deep tensions between Clinton supporters and those loyal to her primary opponent Bernie Sanders.

Sanders was closing the night, speaking just after Massachusetts. Sen. Elizabeth Warren.

Sanders, comparing Trump’s stances and statements to Clinton’s record, said in remarks released before his speech, “By these measures, any objective observer will conclude that – based on her ideas and her leadership – Hillary Clinton must become the next president of the United States. The choice is not even close.”

Warren, a favorite of liberals, has emerged as one of the Democrats’ toughest critics of Trump, and she kept up her attacks on his character and business record as she delivered the night’s keynote address.

“Donald Trump has no real plans for jobs, for college kids, for seniors,” she said. “No plans to make anything great for anyone except rich guys like Donald Trump.”

The cheers from the audience masked real tensions that had spilled into the convention hall and onto the streets of sweltering Philadelphia earlier in the day.

Sanders’ supporters arrived at the convention infuriated over leaked emails showing the Democratic National Committee had favored Clinton in the primaries, despite vows of neutrality.

hey scored the resignation of party chair Debbie Wasserman Schultz, but still erupted in chants of “Bernie” and booed Clinton the first several times her name was mentioned during the convention program. Outside the convention hall, several hundred Sanders backers marched down Philadelphia’s sweltering streets with signs carrying messages such as “Never Hillary.”

Sanders and his team spent much of Monday trying to keep backers from protesting on the convention floor. He sent urgent emails and text messages urging them to avoid protests on the convention floor. The Clinton campaign opened up speaking spots for his supporters.

An array of office holders and celebrities hammered home the call for unity, with singer Paul Simon singing his “Bridge Over Troubled Water” as delegates linked arms and swayed to the music.

Former President Bill Clinton smiled and clapped from the audience.

Mrs. Obama was one of the night’s standouts. While she has often avoided overt politics during her nearly eight years in the White House, her frustration with Trump’s rise was evident. She warned that the White House couldn’t be in the hands of someone with “a thin skin or a tendency to lash out” or someone who tells voters the country can be great again.

“This right now, is the greatest country on earth,” she said.

Clinton’s campaign hoped the nighttime line-up would overshadow a tumultuous start to the four-day convention. The hacked DNC emails fed the suspicion of Sanders’ supporters and sapped Clinton’s campaign of some of its energy following a well-received rollout Sunday of her running mate, Virginia Sen. Tim Kaine.

Campaigning in North Carolina, Trump seemed to revel in the Democrats’ commotion, telling supporters that Clinton made a mistake by not choosing a more liberal running mate to appease Sanders’ base. “Crazy Bernie’s going crazy right now,” he said.

But in Philadelphia, Delegates waved “Love Trumps Hate” signs and leapt to their feet as immigration supporters, gay rights advocates, and labor leaders took the stage.

Comedian-turned-Sen. Al Franken, a Clinton supporter, and actress Sarah Silverman, a Sanders supporter, made a joint appearance to promote party unity.

“I am proud to be part of Bernie’s movement,” Silverman said as the crowd roared. “And a vital part of that movement is making absolutely sure Hillary Clinton is our next president of the United States.”

Trump was a frequent target throughout the night, though the jabs were often more mocking than mean. The tone was a sharp contrast to the Republican convention, where the attacks against Clinton was bitingly personal, including chants of “Lock her up.”

Wasserman Schultz had planned to be among those taking the stage, despite the email hacking controversy. But she stepped aside, bowing to pressure from Democrats who feared the mere sight of her on stage would prompt strong opposition from Sanders’ backers.

The outgoing chairwoman did watch the gathering from a private suite at the arena.

Clinton’s team hoped Wasserman Schultz’s resignation — along with an apology from the DNC to Sanders and his supporters — would keep the convention floor calm.

Discussions between the two camps prompted Sanders to send emails and text messages to supporters asking them not to protest.

“Our credibility as a movement will be damaged by booing, turning of backs, walking out or other similar displays,” Sanders wrote.

The party infighting had echoes of last week’s Republican convention, where some major GOP leaders voiced their displeasure with Trump and others didn’t even show up. Clinton promised a stark contrast to the GOP gathering, saying she planned to highlight “success stories” and flesh out details of her proposed policies.

Sanders was a relatively unknown Vermont senator when he decided to challenge for the Democratic nomination. He stunned the Clinton campaign with his broad support among young people and liberals, as well as his online fundraising prowess. But he struggled to appeal to black voters and couldn’t match the former secretary of state’s ties to the Democratic establishment.

The controversy over some 19,000 leaked DNC emails, however, threatened to complicate those plans. The correspondence, posted by WikiLeaks over the weekend, showed top officials at the supposedly neutral DNC favoring Clinton over Sanders in the presidential primaries.

Clinton campaign officials blamed the hack, which is now being investigated by the FBI, on Russian military intelligence agencies. The campaign also accused Moscow of trying to meddle in the U.S. election and help Trump, who has said he might not necessarily defend NATO allies if they are attacked by Russia.

Associated Press writers Kathleen Hennessey, Catherine Lucey, Kathleen Ronayne and Julie Bykowicz in Philadelphia, Lisa Lerer in Charlotte, North Carolina, contributed to this report.