DES MOINES — Elizabeth Warren and Bernie Sanders are locked in a fierce competition to win over Iowa liberals. Joseph R. Biden Jr. and Kamala Harris are scrambling to avoid a humiliating fourth-place finish — or worse — in the Iowa caucuses. And Pete Buttigieg and Amy Klobuchar are angling for surprisingly strong results to catapult their candidacies.
As Democrats converge on Des Moines on Friday night for the party’s biggest Iowa political event of the fall, the state’s political contours are coming into increasingly sharp relief, with these three political dynamics likely to define the last 94 days before the first-in-the-nation presidential nominating contest.
The dinner is occurring on one of the most consequential days of the race so far, with Ms. Warren, under pressure from other candidates over how she would pay for “Medicare for all,” finally introducing a long-awaited, $20.5 trillion proposal that immediately drew a fierce attack from her chief rival, Mr. Biden.
Now called the Liberty & Justice Celebration, the dinner served as a springboard for Barack Obama’s surprise victory over Hillary Clinton in Iowa’s 2008 caucuses, and most top-tier campaigns are planning big showings.
The Biden, Buttigieg and Warren campaigns have each bought large sections of the 16,000-seat Wells Fargo Arena for supporters to cheer their candidates. Mr. Sanders, while speaking at the event, is bringing no supporters, electing to lead them in a march outside instead, part of a pattern of the independent senator’s antipathy toward Democratic Party functions.
At the same time, the candidates have been wooing voters with bus tours, rallies and town hall-style events. Ms. Harris, the California senator whose campaign has been flagging, has taken to cooking Sunday night dinners in supporters’ homes and plans to spend Thanksgiving in the state.
The surge in attention on Iowa coincides with a more contentious phase of the race, marked by aggressive campaigning and an increased willingness to go on the offensive.
Mr. Sanders, the senator from Vermont, and Mr. Biden, the former vice president, have resumed their attacks on each other, with back-and-forth sniping in the last week about Medicare for all and super PACs. Mr. Buttigieg and Ms. Klobuchar have shown an increased willingness to go after Ms. Warren, the senator from Massachusetts.
Lower-tier candidates looking to energize their campaigns have also been more pugnacious: Representative Tulsi Gabbard of Hawaii, for instance, has amped up her criticisms of the Democratic National Committee, the news media and even Mrs. Clinton, who is not in the race.
The crowded and diverse field — there are still 17 candidates — has proved challenging for contenders outside the top tier. While nine have qualified for the party’s November debate in Atlanta, just four are guaranteed a spot for the December debate in Los Angeles. Even among those onstage, it has become increasingly difficult for anyone outside the top half-dozen candidates to attract attention.
A poll taken this week of likely caucusgoers by The New York Times and Siena College shows the top four candidates locked in an extraordinarily tight race. Ms. Warren held a narrow advantage, with the support of 22 percent of voters, while Mr. Sanders drew 19 percent and Mr. Buttigieg 18 percent. Mr. Biden, who entered the race a front-runner, had the backing of 17 percent of likely caucusgoers, much weaker than his position in national polls.
For Democrats who had been inclined to support Mr. Biden but now find themselves shopping around, that means the moderate choices are limited to Mr. Buttigieg, the mayor of South Bend, Ind., and Ms. Klobuchar, the senator from Minnesota, with other would-be options like Senator Cory Booker of New Jersey falling out of the conversation.
Susan Swift, a 58-year-old yoga teacher from Dubuque, said at a Biden event Wednesday that even after watching nine months of campaigning she is still trying to decipher the field.
Ms. Swift said she liked the former vice president for “his experience,” but had become more impressed with Mr. Buttigieg the more she had seen him.
“Did you see the pluck that that guy had in the last debate?” she said. “Seriously? I was like, ‘You just won my heart.’”
Conversations this week with 24 of Iowa’s 99 Democratic county leaders revealed moderate Democrats moving from Mr. Biden toward Mr. Buttigieg and Ms. Klobuchar, who the county officials said have benefited from strong debate performances and repeated trips to the state.
Mr. Biden drew his early support from name recognition and good will dating from his connection to Mr. Obama, but as other candidates have gained exposure, Mr. Biden’s standing has fallen.
“I think caucusgoers are writing Joe off,” said Gary Gelner, the Democratic chairman in Hancock County. “Age and bad press are wearing him thin.”
Ms. Warren is also attracting attention from some voters who support Mr. Biden.
Betty Heideman, 85, of Fort Dodge, said she liked Mr. Biden but wanted to “hear a lot more from him to know if he’s the strongest guy — strongest person — in it to win.” About Ms. Warren, she said, “She’s not afraid to speak up.”
Mr. Sanders, who fought Mrs. Clinton to a draw in Iowa four years ago, has struggled to retain support in the party’s most liberal pockets. Some of his anti-establishment backers have gravitated to candidates even more outside the mainstream, like the entrepreneur Andrew Yang and Ms. Gabbard.
Zach Simonson, the Democratic chairman in Wapello County, backed Mr. Sanders in 2016 and said he was now torn between Mr. Sanders and Ms. Warren.
“I was all in for Bernie in 2016, but with Warren in the race, some of the weaker parts of his candidacy are magnified,” Mr. Simonson said. “He’s got a very reasonable critique of the national Democratic Party institution, but from campaigning so much on the outside, I don’t know if he’ll be ready to take the role of national standard-bearer for all Democrats after the convention.”
Mr. Biden made it clear how important Iowa was to his campaign, as he continues to slip behind.
“I’m asking for your help,” he told an older crowd who had come to see him on Thursday in Fort Dodge. “Commit to caucusing for me on Feb. 3.”
Asked by someone in the audience to list the “five most important planks” of his campaign platform that voters should know before they decide to caucus for him, Mr. Biden grew impassioned, quickly ticking off reasons including “No. 1, begin to treat people with dignity.”
Speaking to reporters afterward, he expressed confidence in his Iowa operation. “I think we have one of the best organizations in this state and around the country,” he said.
But if Iowa typically helps set the narrative for the primary season, its voters are poised to play perhaps their most significant role yet: After months of a race in flux, the results in Iowa could finally bring clarity to the race. Democratic officials expect the state to help winnow the field, and to reveal the preferences of Midwestern Democratic voters in a red-leaning state.
While Mr. Obama used the state party dinner — then named for Andrew Jackson and Thomas Jefferson — to catapult him to the White House, this year’s field has a tougher challenge. Recent Iowa presidential cattle calls have not resulted in any tangible change in the race.
With so many candidates speaking, it can be difficult to deliver a memorable performance. There is a significant advantage in speaking early in the program — at the Polk County Steak Fry in September, Representative Tim Ryan, who went last, found himself delivering a speech as attendees fled a late-arriving rainstorm. (Mr. Ryan ended his campaign last week.)
Gov. Steve Bullock of Montana drew the 14th and final speaking slot Friday. His campaign quickly announced he would deliver the event’s “keynote address.”