DES MOINES, Iowa—Thirteen Democratic presidential candidates addressed roughly 13,000 Democrats at the Wells Fargo Arena here, hoping to replicate Barack Obama’s performance at a similar event 12 years ago that started his path to the party’s nomination.

In the crowded 2020 field, with each candidate getting 10 minutes over the course of more than four hours, there was no single breakout performance like Mr. Obama’s.

Here are several moments that mattered with less than 100 days until the first nominating contest:

“I’m here to launch the era that must come next.”

South Bend, Ind., Mayor Pete Buttigieg almost immediately invoked Mr. Obama, pitching himself as the young Washington outsider capable of uniting the country after what is likely to be a divisive general election. “The first time I came to this state was as a volunteer, to knock on doors for a presidential candidate—a young man with a funny name,” he said.

Staff for Pete Buttigieg promote their candidate at the Iowa Democrat Party's Liberty & Justice Dinner. Photo: Michael Bucher/The Wall Street Journal

Mr. Buttigieg’s supporters took some cues from Mr. Obama’s 2008 campaign. Clad in bright yellow and lights, they clapped thunder sticks together loudly and took over the largest section of the arena.

“We knew the stakes were high then. The stakes are colossal now,” Mr. Buttigieg said.

Hundreds of his backers, who deemed themselves the “barnstormers,” traveled from around the country to see Mr. Buttigieg. Lynn Wilson, a nurse from Rochester, Minn., described him as “hope personified.”

Mr. Buttigieg has been enjoying a bump in recent polling. A Friday New York Times/Siena College poll had Vermont Sen. Bernie Sanders, Mr. Buttigieg and former Vice President Joe Biden all effectively tied among Democratic primary voters in Iowa, close behind Sen. Elizabeth Warren of Massachusetts.

“Anyone who comes on this stage and tells you to dream small and give up early is not going to lead our party to victory.”

Ms. Warren, who rarely veers off her usual campaign speech, made a more forceful case for the “big structural change” her campaign is centered on. With the moderates in the race targeting her more aggressively, Ms. Warren used part of her speech to respond to her critics.

Supporters of Sen.Elizabeth Warren cheer her on with a large banner at the Wells Fargo Arena. Photo: Michael Bucher/The Wall Street Journal

“Look, anyone who comes on this stage and doesn’t understand that we’re already in a fight is not the person who is going to win that fight,” she said.

“I’m not running some consultant-driven campaign with some vague ideas that are designed to not offend anyone,” Ms. Warren added.

Mr. Biden—along with Mr. Buttigieg and Minnesota Sen. Amy Klobuchar, who are all seeking to win over more moderate Midwestern voters—have been going after Ms. Warren lately over her support for a government-run health-care plan that would eliminate private insurers.

“Unlike others, I’ve never represented a corporation.”

California Sen. Kamala Harris, who has been fading in polls as her campaign goes all-in on Iowa, emphasized her experience as a prosecutor, including a line that could be seen as a shot at Ms. Warren.

“I’ve never represented a special interest,” Ms. Harris said. “I’ve always represented the people.”

Sen. Kamala Harris of California got one of loudest receptions from the crowd. Photo: Jack Kurtz/Zuma Press

Ms. Warren’s work for corporations while she was a law professor has come under scrutiny from some liberals. As an expert on bankruptcy, she made hundreds of thousands of dollars representing corporate clients. Her campaign has disclosed 50 cases she was involved in on its website.

Ms. Harris, whose campaign was hoping to use her speech Friday to reboot her candidacy, got one of loudest receptions from the crowd.

“This is like a general election in a primary.”

Mr. Biden, who has been fighting to hold on to his front-runner status, continued to stress to caucus-goers that he was the best candidate to take on President Trump, saying Republicans have already turned their firepower on him.

Former Vice President Joe Biden said he was the best candidate to take on President Trump. Photo: Michael Bucher/The Wall Street Journal

“Folks, it’s the reason he’s spending so much money with his henchmen in running ads against me in a primary. This is just like a general election, in a primary,” Mr. Biden said. “He knows I will beat him like a drum.”

Mr. Trump is facing an impeachment inquiry in part over efforts to press Ukraine to launch an investigation into Mr. Biden and his family. Mr. Trump and the GOP have accused Mr. Biden’s son Hunter Biden of profiting off his father’s name.

“I see you, I love you.”

New Jersey Sen. Cory Booker received a standing ovation for his speech pushing unity. He began by talking about a mentor whose last words were “I see you, I love you.”

Sen. Cory Booker of New Jersey acknowledges supporters after speaking during the Iowa Democratic Party Liberty & Justice Celebration. Photo: Joshua Lott/Getty Images

“I hear the pundits say this about who’s polling the best or who has the most money or who can best deliver a shot against another Democrat on a stage,” Mr. Booker said. “This is going to be best decided by who can best pull us to our common aspiration, who can best inspire us to be the truth of who we are.”

So far, Mr. Booker’s positive message has failed to garner strong support. He averages in the low-single digits in national and early state polls.

Other low-polling candidates failed to even get a proper introduction. Former Maryland Rep. John Delaney was introduced with photos of Montana Gov. Steve Bullock on the screens behind the stage. When it was Mr. Bullock’s turn, the announcer introduced him as Mr. Booker.

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