New York Mayor Bill de Blasio jumped into the increasingly crowded White House race Thursday, defying hostile media and dismal polls to cast himself as the Democrats' best chance of unseating the "con artist" Donald Trump in 2020.

The 23rd prospective Democratic challenger to Trump, de Blasio kicked off with a frontal attack on the Republican president, dubbing him "Con Don" for claiming he is on the side of working Americans.

"Donald Trump must be stopped," he declared in a video announcing his candidacy. "I know how to take him on."

Doubling down in an interview on ABC's "Good Morning America," de Blasio charged: "Donald Trump is playing a big con on Americans."

"Every New Yorker knows he's a con artist," he said. "Working Americans deserve better and I know we can do it because I've done it here in the largest, toughest city in this country."

Trump, meanwhile, skewered de Blasio in an early morning tweet as "the worst mayor in the US."

"He is a JOKE, but if you like high taxes & crime, he's your man. NYC HATES HIM!"

De Blasio had been exploring a possible run for months, traveling to early voting states like Iowa and South Carolina.

His campaign has so far been met with widespread derision, with polls giving the former vice president Joe Biden a commanding lead among Democratic contenders, followed by the liberal senator, Bernie Sanders.

Democratic polling has been particularly humbling at home.

An eye-popping 76 percent of New York City voters said he should not enter the 2020 race, according to a Quinnipiac University poll last month.

Local papers have taunted him for a lack of charisma and Thursday's front page of the New York Post tabloid was particularly scathing: a photo montage of people laughing hysterically above the headline "De Blasio runs for president."

- Perpetual underdog -

De Blasio himself touts a string of accomplishments as mayor: he has introduced free universal pre-kindergarten and paid sick leave, and early this year rolled out a plan to guarantee health care for all New Yorkers.

"We're putting money back in the hands of working people," said the 58-year-old, who was first elected in 2013 and comfortably re-elected two years ago.

Bill de Blasio 2020/AFP / -In this image taken from a video, New York City Mayor Bill de Blasio announces his candidacy for the 2020 US presidential elections, vowing to put "working people first"

Yet despite the truism that the job of New York mayor is the second toughest in America after that of president, de Blasio -- sometimes nicknamed "Big Bird" for his lanky, 6-foot, 5-inch (1.97-meter) frame -- is one of the few people openly confident of his presidential chances.

Asked about the numbers during his TV interview, de Blasio replied: "I think you'll agree that the poll that actually matters is the election."

De Blasio succeeded billionaire Michael Bloomberg on the promise of reducing the city's glaring inequalities.

Since Trump came to power, de Blasio has denounced the Republican president's hardening of immigration policy and his decision to pull the United States out of the Paris climate accord.

"We must deal with global warming now," de Blasio told "Good Morning America," pledging support for the Green New Deal, a proposal offered by progressive Democrats that would dramatically shift the United States away from fossil fuels toward renewable energy.

A former supporter of Nicaragua's Sandinistas, de Blasio was closer to the liberal Sanders than to Hillary Clinton during his party's 2016 nomination battle.

De Blasio is married to Chirlane McCray, an African-American woman who for decades identified as a lesbian.

He remains popular in the black community, but Hispanics are divided and whites mostly view him unfavorably.

Several current and former aides spoke out in unusually harsh terms about his expected White House bid.

But the mayor -- who likes to cast himself as a perpetual underdog -- appears to have brushed off the criticism, confiding recently that the only advice that matters is his wife's.