Mayor de Blasio didn’t even register in a new Iowa poll that shows former Vice President Biden’s support slipping but Pete Buttigieg surging among the field of Democratic presidential hopefuls in Iowa.

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.

​”​There’s always been a question mark as to how many (candidates) can get any real traction,” ​said J. Ann Selzer, the president of Selzer & Co., which conducted the survey. ​”​And we gave them every opportunity to show that they have some kind of constituency here. But there’s a fair number who, their constituency just isn’t very big.”

​De Blasio will attend a major Democratic Party fundraiser Sunday evening in Cedar Rapids, skipping the Puerto Rican Day Parade, the first sitting mayor to miss the celebration.

Biden is still the front-runner with 24 percent of the support of likely caucus-goers, but that’s down from December’s survey when he registered 32 percent of support, the survey said.

The race for second place is a statistical dead heat with Sen. Bernie Sanders at 16 percent, Sen. Elizabeth Warren amassing 15 percent and Buttigieg, the mayor of South Bend, Ind., gaining 14 percent.

The survey shows both Warren and Buttigieg making strong gains after polling at just 9 percent and 1 percent, respectively, in March.

Sen. Kamala Harris of California is the only other candidate among the field with a significant level of support with 7 percent.

T​he poll was taken between June 2 and June 5​, before Biden flip-flopped on his stand on the Hyde Amendment, which bans federal funds for most abortions.

Last Thursday, he came out against the amendment.

The Iowa caucuses will be held Feb. 3, 2020.

The poll surveyed 600 likely Democratic caucus-goers. It has a plus/minus 4 percent margin of error.