This was supposed to be the feel-good convention, a celebration of unity and hopeful visions that would contrast with the displays of disunity at the Republican convention in Cleveland last week. But for much of Monday, that goal appeared in doubt, as Democrats turned on one another and demonstrated their own disunity that disrupted the script of Hillary Clinton’s campaign team.

It took first lady Michelle Obama to begin to turn the convention in a different direction. Doing for Clinton what Bill Clinton did for her husband, Obama made a passionate case for Clinton’s candidacy that the former secretary of state has not been able to make as effectively for herself. “In this election,” she said, “I’m with her.”

Obama’s speech brought the Democrats to life and set the stage for two more speakers — first Sen. Elizabeth Warren (Mass.) and finally Sen. Bernie Sanders (Vt.) — who tore into Donald Trump and championed Clinton as the person to deny the Republican nominee the White House.

For the final hour of the day, Obama, Sanders and Warren reminded Democrats of their common interests and their common goal of defeating Trump, rather than dwelling on the long and divisive nominating battle that exposed fault lines between the establishment and the grass roots.

Monday’s opening day had included the unceremonious removal of Democratic National Committee Chair Debbie Wasserman Schultz from the convention program; an unprecedented apology from the new leadership of the DNC to Sanders and his supporters after leaked emails revealed an institution that had clearly strayed from its pledge of neutrality in the nomination battle; and cascades of boos by Sanders’s delegates and supporters when they were urged to get behind Clinton in her campaign against Trump.

All that was the prelude to the prime-time program. Collectively, Obama, Sanders, Warren and the night’s other main speaker, Sen. Cory Booker (N.J.), projected the kind of high voltage a political party needs when it is in danger of losing its focus. It was more wattage than the Republicans were able to put on their stage in the early days of the Cleveland convention, even accounting for the performances of Trump’s children and his wife.

But more important was what they said and how it could start to wipe away the hard feelings of a year of conflict and competition with Sanders and a weekend of embarrassment over the contents of the leaked emails.

Obama was greeted by a huge chorus of cheers that echoed across Wells Fargo Center, and she delivered a ringing endorsement of Clinton as a parent and a potential president.

“I am here tonight because in this election there is only one person who I trust with that responsibility, only one person who I believe is truly qualified to be president of the United States, and that is our friend Hillary Clinton,” she said.

Warren had the unenviable task of following Obama. She praised Sanders and then turned to what has become her specialty, a slashing attack on Trump. She said Trump’s America would be one of “fear and hate” and in danger of breaking apart.

First lady Michelle Obama addressed the Democratic National Convention in Philadelphia July 25. Here are some highlights from that speech. (Video: Deirdra O'Regan/The Washington Post; Photo: Jabin Botsford/The Washington Post)

She described him as a selfish businessman who would reward the wealthy at the expense of everyone else. What kind of man is Trump, she asked, and delivered her own answer: “A man who should never be president of the United States.”

Sanders’s advisers said before he took the stage that he was on a mission of unity, not further division, after a day when his supporters seemed unwilling to follow him that far. He won an enormous ovation as he arrived on the stage, the longest and loudest of the day and of any speaker in Cleveland last week.

For Clinton, Sanders could not have given a more appealing speech. Ticking through what he called the critical issues of the election, he said: “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.”

He expressed disappointment but no bitterness at how the Democratic race had turned out, and he closed with the kind of clear statement Clinton’s team has been looking for ever since the primaries ended. “Hillary Clinton will make an outstanding president, and I am proud to stand with her tonight.”

This was a night that ended in signs of unity, but in Sanders and Warren on the one hand, and Obama and Booker on the other, the pairings highlighted tension between two parts of the party that see the world and the issues from differing perspectives and are now being called upon to join forces to stop Trump from becoming president.

And what was happening throughout the day — on the streets, at some delegation meetings, at a raucous rally for Sanders and at times even on the convention floor — was a vivid reminder that the Democratic Party’s establishment continues to coexist uneasily with those in the anti-establishment left, who remain wary and resistant to Clinton, however much they despise Trump.

One indication of how tense things were came in the late afternoon. With the potential for continued disruptions on the convention floor from Sanders’s followers, the senator from Vermont sent an email to all his delegates, pleading with them to show courtesy.

“Our credibility as a movement will be damaged by booing, turning of backs, walking out or other similar displays,” he wrote. “That’s what the corporate media wants. That’s what Donald Trump wants.”

After Saturday’s successful introduction of Sen. Timothy M. Kaine (Va.) as Clinton’s vice-presidential running mate, the Clinton team had good reason to expect a smooth-running convention. Their talking points were clear: They would provide something positive to contrast with the GOP gathering in Cleveland, and the delegates, despite a bruising nomination contest, would find Trump so distasteful that they would quickly rally behind their nominee-in-waiting.

But as that Clinton-Kaine rollout was taking place, another story was unfolding that would suddenly shift the spotlight to the embarrassing details of internal DNC emails that were posted on WikiLeaks on Friday but not fully digested until Sunday.

The wall of unity quickly began to crack. Wasserman Schultz’s position as party chair became untenable at a convention already divided between the Clinton and Sanders forces. The ensuing uproar forced Wasserman Schultz, a congresswoman from Florida, to announce that she would step down at the end of the convention. When it was clear that wouldn’t satisfy the Sanders forces, she gave up the right to gavel the convention to order.

The unyielding stance of many of Sanders’s supporters produced the same tenor on the convention floor in the early afternoon as that on the opening day in Cleveland, when the “never Trump” forces were gaveled down as they sought a roll-call vote on the adoption of the rules. Clinton’s challenge is to bring as many of those Sanders supporters to her side as she can and motivate them to vote in November.

For the Democrats, the route to unity is not unlike that of the Republicans: demonizing the opposition. Last week it was Republicans attacking Clinton. On Monday night it was Democrats — whether for Clinton or Sanders — attacking Trump.

But Michelle Obama added a positive case for Clinton, and the mood on the convention floor seemed to change almost instantly with her performance.

That could mean a better three nights ahead than the Clinton team might have thought Monday afternoon. But what played out here the past two days won’t disappear with a round of speeches. Monday’s final hour was a start, but Clinton still has work to do — inside the hall and especially outside, to the audience watching on television.