WASHINGTON — New York City Mayor Bill de Blasio will declare his bid for the presidency on Thursday, a campaign spokesperson said Wednesday, joining the almost two dozen other candidates already competing for the Democratic nomination.

De Blasio will make the formal announcement Thursday morning and then travel to Iowa and South Carolina for multiple stops over four days. His wife, Chirlane McCray, who has been a highly visible presence and close adviser during his six years at City Hall, will join him for part of the trip.

A Facebook post from the Woodbury County Democratic Party in Iowa announcing that de Blasio would appear at an event Thursday as the first stop on his presidential tour let the cat out of the bag early before his formal declaration. The post was later deleted.

The mayor plans to highlight his record of liberal accomplishments in the nation’s largest city, including enacting universal pre-kindergarten, raising the minimum wage to $15 an hour, and overseeing a drop in crime to an all-time low.

De Blasio is not particularly popular back home, nor in early surveys of Iowa and New Hampshire, which vote first in the primary process. His popular predecessor, Michael Bloomberg, opted out of a 2020 run.

But allies of de Blasio, who was easily re-elected in 2017 despite a testy relationship with the local press corps and an FBI investigation that eventually cleared him, argue he has as much or more executive experience as any candidate in the 2020 field and a record of actually doing things other candidates have only talked about.

"Because he has such a present press corps in a tabloid city, we've seen him up close and in an aggressive and unflattering light, but if you look at his actual record of achievement, it's quite lengthy,” said Rebecca Katz, a Democratic strategist and former top de Blasio aide. "Yes, there's an argument to be made about whether he should be running for president or not, but he is certainly qualified."

With an estimated 8.6 million residents, New York City has a bigger population than 38 states, including Washington, Colorado and Montana, whose governors or former governors are also running for president.

And New York is about 85 times larger than South Bend, Indiana, whose mayor, Pete Buttigieg, has become an unlikely top-tier candidate. (The city council district de Blasio used to represent in Brooklyn is bigger than South Bend.)

And given the city’s unique global importance, de Blasio has overseen a police force involved in anti-terrorism and hosted world leaders at the United Nations, which is headquartered in the city.

Still, de Blasio has struggled in past attempts to build a national progressive following.

He conspicuously held off on endorsing Hillary Clinton in 2016, even though he was once the manager of her Senate campaign, saying he wanted to host candidate forums in Iowa to force all candidates to prove their progressive bonafides. The forums never materialized and de Blasio ended up endorsing Clinton.

De Blasio is the last major candidate expected to enter the 2020 Democratic field, though surprise additions are always possible.

There will only be room for 20 candidates in the first debate next month, hosted by NBC News, MSNBC and Telemundo. Later-entry candidates like de Blasio may have difficulty qualifying.