New York Mayor Bill de Blasio has announced he is pulling out of the Democratic race for the White House.
"I have reached a point where I feel I have contributed all I can to this primary," the 58-year-old said in an email to supporters.
Observers say his campaign had failed to take off within a wide field of Democrats seeking to be selected as the party's presidential candidate.
Despite him dropping out 19 more remain in the race.
Mr De Blasio won a landslide victory in 2013 to become New York's first Democratic mayor in a decade.
He implemented a programme of free universal pre-school and made police wear body cameras in the most populous city in the US. Mr de Blasio was rewarded for his efforts at the polls: re-elected in 2017 with more 66% of the vote.
Still, New Yorkers did not get behind their mayor's presidential bid. A Quinnipiac poll from one month before he announced found that 76% of the city did not want him to run.
Announcing his decision to leave the race, Mr de Blasio thanked supporters, describing his presidential campaign as a "profound experience".
President Donald Trump tweeted about Mr de Blasio's announcement, saying sarcastically it was "really big political news".
Oh no, really big political news, perhaps the biggest story in years! Part time Mayor of New York City, @BilldeBlasio, who was polling at a solid ZERO but had tremendous room for growth, has shocking dropped out of the Presidential race. NYC is devastated, he’s coming home!— Donald J. Trump (@realDonaldTrump) September 20, 2019
Mr de Blasio told MSNBC that a "central reason" for his decision was the Democratic Party's rules for qualifying for televised debates.
"The bar is so high so early that for a lot of us - clearly, some of my fellow chief executives, governors - couldn't make that cut," he said.
He failed to qualify for a debate earlier this month that featured the 10 leading candidates for the party's nomination.
A short and ill-fated run
Bill de Blasio's presidential campaign has been described as "quixotic" - but even Cervantes' hero had a few imagined victories before the end. The New York mayor was a late entry to the race, started at the bottom of the pack and stayed there.
De Blasio ran on a progressive platform, but progressives didn't like him. No one seemed to like him much. In fact, the New Yorker's negatives were higher than any of the other candidate in the field.
Perhaps Democratic voters weren't that keen on trading the current pugilistic New Yorker in the White House for one of their own.
There are now 19 Democrats left in the running, with former Vice-President Joe Biden currently ahead in the polls, followed by left-wing senators Elizabeth Warren and Bernie Sanders.
The rest of the Democratic contenders have polled in single figures in most opinion polls.