The poll showed that Biden is the first choice for 24% of would-be Democratic caucusgoers, compared with 16% for Sanders, 15% for Warren and 15% for Buttigieg.

In March, before Biden formally entered the race, he and Sanders held a commanding lead, with 27% and 25% support according to The Register’s polling, which has long been judged by campaigns as the best in the state. At the time, Warren was polling at 9% and Buttigieg at 1%.

Sen. Kamala Harris of California was at 7% support in both surveys. Sen. Amy Klobuchar of Minnesota and former Rep. Beto O’Rourke of Texas, both at 2%, were the only other candidates above 1% in the new poll.

The latest poll results reflect an enormous and unsettled field in which just a handful of candidates seem to be breaking through to voters. Just five of the 23 candidates in the race registered more than 2% support while nine candidates — including Sen. Kirsten Gillibrand of New York and Mayor Bill de Blasio of New York City — registered zero percent support.

Buttigieg, speaking before an event for northeastern Iowa Democrats in Cresco, said the poll validated his campaign strategy to date.

“It shows that campaigning works,” he said. “We’ve invested a lot of time and a lot of effort, not just nationally but getting to be known in Iowa and obviously that’s led to some growth.”

The poll comes on the eve of Iowa’s first major political event of the summer campaign season — a state Democratic Party gathering Sunday in Cedar Rapids that 19 of the candidates are expected to attend.

Biden is skipping the event, electing to remain in Washington before a two-day Iowa swing beginning Tuesday, when President Donald Trump will also be in the state. Biden’s campaign is emerging from a rocky stretch in which he reversed a long-held position against federal funding for abortions after facing intense pressure from fellow Democrats and within his own campaign.

For months, Democratic officials in Iowa have said Biden’s support in polls overrepresents the level of organization or excitement for his candidacy among the party’s most committed activists.