"This time we've got a whole lot of candidates and I don't think anybody is going to reach 50 percent". Bernie Sanders at 16 percent, Sen.
Seven other candidates planned to speak at the event in the capital.
Biden is the first choice of 24 per cent of likely Democratic caucus-goers in Iowa, the state that kicks off the presidential nominating race next February, in the Des Moines Register/CNN/Mediacom Iowa Poll.
Mr Sanders, a USA senator, is the first choice for 16 percent of respondents, while Ms Warren, also a U.S. senator, and Mr Buttigieg, the mayor of South Bend, Indiana, are at 15 percent and 14 percent, respectively.
Both candidates hold 14 per cent support, only one per cent behind Sanders who earned 15 per cent in the poll. "And some of these candidates who've been under the radar start to surface and compete with Joe Biden".
"We're starting to see the people who are planning to caucus start to solidify". Biden now supports federal funding for abortion services after opposing it for decades.
"Biden and Sanders have fallen in first and second in almost every poll conducted since March", Newsweek reported.More news: Facebook's GlobalCoin to go live as early as in June
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"It's like with the vitriol and the hatred and all the bad things people say - he seems to be coming out fresh", Patti Thacker, a Cedar Rapids poll respondent said about Buttigieg in the Register report.
A spokesperson from The Register said the poll methodology changed from its last few surveys.
De Blasio, who's been in Iowa campaigning over the weekend, and Wayne Messam, the mayor of Miramar, Fla., were the only two candidates in the field of 23 not listed as either a first or second choice for president in the Des Moines Register/ CNN poll released late Saturday.
That makes the results of this poll not directly comparable to past polls of the presidential field, the Register said.
The poll was conducted between June 2 and 5, with a margin of error of plus or minus 4 percentage points. In March, the first time he appeared in an Iowa poll, he barely caused a blip among voters.
Indeed, 36 percent of those polled said they would be willing to consider Booker even if they have yet to name him as the first or second choice.