DES MOINES — Senator Elizabeth Warren of Massachusetts is the new Iowa polling leader, narrowly in first place ahead of former Vice President Joseph R. Biden Jr., according to a new poll of the state from The Des Moines Register and CNN.
The poll showed that Ms. Warren was the first choice for 22 percent of would-be Democratic caucusgoers, a significant increase from the 15 percent support she held in June, when The Register last polled the state. Mr. Biden dropped from a first-place June showing of 24 percent to 20 percent. The result left the two in a statistical tie, well ahead of the rest of the pack.
The poll is the latest evidence of Ms. Warren’s political rise in the 2020 race. Alone among the 2020 candidates, her campaign stops have become bona fide events, with 20,000 people attending a speech in Manhattan this week and 2,000 turning out in Iowa City on Thursday night.
Senator Bernie Sanders of Vermont placed third with 11 percent, the second consecutive poll from The Register in which his campaign has seen precipitous decreases in support. Mr. Sanders, who placed in a statistical tie with Hillary Clinton in the state’s 2016 contest, had 25 percent support in the paper’s March poll and 16 percent support in June.
Mayor Pete Buttigieg of South Bend, Ind., placed fourth in The Register’s poll, with 9 percent. He had 14 percent in The Register’s June poll and has fallen in other surveys of the state since then before launching a television advertising campaign here after Labor Day.
The gains by Ms. Warren come largely at the expense of Mr. Sanders. His polling drop-off comes as his campaign has reordered staff in early nominating states in an effort to reboot his campaign.
Senator Kamala Harris of California was fifth overall with 6 percent support. Senator Cory Booker of New Jersey and Senator Amy Klobuchar of Minnesota each had 3 percent support. Four candidates were the first choice of 2 percent of likely Iowa caucusgoers.
In addition to leading the field, Ms. Warren also has the most room for growth in the field — 71 percent of Democrats surveyed said she was their first or second choice or they were open to backing her, the poll found. Mr. Biden was next, being considered by 60 percent of Iowa Democrats. Of the rest of the field, only Mr. Buttigieg and Ms. Harris were being considered by more than half the Democratic electorate.
The dynamics are far from set: Just one in five likely Democratic caucusgoers said their minds were made up, and 63 percent said they could still be persuaded to support a different candidate.
The poll comes after 17 Democratic presidential candidates appeared Saturday at the Polk County Steak Fry, an annual political event that drew 12,000 activists and voters to a Des Moines park for several hours of political speeches, campaign singalongs and freshly grilled meats.
The poll, like the Steak Fry event, illustrated the increasingly condensed nature of the 2020 Democratic presidential contest. The poll found just five candidates registering more than 3 percent support, while those who braved the drizzling conditions and threat of thunderstorms congregated around the candidates who emerged hours later atop the polls.
The event’s largest applause came for Ms. Warren, who repeated a forceful call for President Trump’s impeachment, and Mr. Buttigieg, who was followed by a yellow-clad cadre of highly enthusiastic supporters.
Mr. Biden, whose campaign purchased the largest allotment of Steak Fry tickets, entered the event with a marching band and scores of campaign aides and volunteers. The lower-polling contenders for the most part roamed the grounds of Water Works Park here unencumbered.
Mr. Biden was not the only candidate bringing some flash to the event. Supporters of the former housing secretary Julián Castro danced to a mariachi band, backers of former Representative Beto O’Rourke pushed a boat out into the nearby lake, Ms. Warren took 1,050 selfies and Ms. Klobuchar blasted the music of Prince, a Minnesota hero.
For some, the event may mark one of their last major appearances in the state. Mr. Booker sent out a plea to donors today saying that unless he raises $1.7 million over the next 10 days, he will be unable to remain in the race. He’s not alone in being in danger of running out of cash.