New York City Mayor Bill de Blasio Bill de BlasioOVERNIGHT ENERGY: California seeks to sell only electric cars by 2035 | EPA threatens to close New York City office after Trump threats to 'anarchist' cities | House energy package sparks criticism from left and right EPA threatens to close New York City office after Trump threats to 'anarchist' cities New Year's Eve in Times Square to be largely virtual amid pandemic MORE blasted President Trump Donald John TrumpBiden on Trump's refusal to commit to peaceful transfer of power: 'What country are we in?' Romney: 'Unthinkable and unacceptable' to not commit to peaceful transition of power Two Louisville police officers shot amid Breonna Taylor grand jury protests MORE on Thursday hours after launching his 2020 Democratic presidential campaign, saying “every New Yorker knows he’s a con artist.”

“Right now, the federal government is not on the side of working people. And that’s because Donald Trump is playing a big con on America,” de Blasio said on ABC's “Good Morning America.”

“I call him Con Don. Every New Yorker knows he’s a con artist. We know his tricks. We know his playbook,” de Blasio continued. “I know how to take him on — I’ve been watching him for decades. He’s trying to convince working Americans he’s on their side. It’s been a lie from day one.”

"Every New Yorker knows he's a con artist...I know how to take him on I've been watching him on for decades." New York Mayor @BilldeBlasio speaks on Trump and says he will fight for working class people. https://t.co/ZAfIgoKQBL pic.twitter.com/cvx00hSQm8 — Good Morning America (@GMA) May 16, 2019

“Donald Trump must be stopped,” de Blasio said in a video announcing his White House bid earlier Thursday morning. “I’ve beaten him before and I’ll do it again.”

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Trump, meanwhile, called de Blasio a "JOKE" in a tweet after the mayor announced his presidential candidacy, adding that Democrats are "getting another beauty" in the 2020 field.

The Dems are getting another beauty to join their group. Bill de Blasio of NYC, considered the worst mayor in the U.S., will supposedly be making an announcement for president today. He is a JOKE, but if you like high taxes & crime, he’s your man. NYC HATES HIM! — Donald J. Trump (@realDonaldTrump) May 16, 2019

De Blasio is a frequent critic of Trump, a New York business mogul, and held a news conference in Trump Tower on Monday to promote new regulations curbing energy use by buildings in the city.

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The mayor said the Trump Organization could face fines of around $2 million per year starting in 2030 if its buildings do not reduce their carbon emissions.

He was heckled by Trump supporters during his appearance and then engaged in a heated exchange over Twitter with Eric Trump Eric Frederick TrumpJudge orders Eric Trump to comply with New York AG's subpoena before Election Day Eric Trump uses misleading clip to blast Biden for using teleprompter Melania Trump: Ginsburg's 'spirit will live on in all she has inspired' MORE, the president's son.

De Blasio became the 24th candidate to jump into the already-crowded field of Democratic contenders, vowing to take on the wealthy and big corporations.

"There's plenty of money in this world, there's plenty of money in this country, it's just in the wrong hands," he said in his campaign video.

A Quinnipiac poll from early April found that 73 percent of New York City voters said de Blasio should not run for president, compared to 18 percent who said he should.

“Good Morning America” host George Stephanopoulos George Robert StephanopoulosColbert implores Pelosi to update 'weaponry' in SCOTUS fight: 'Trump has a literal heat ray' Murkowski: Supreme Court nominee should not be taken up before election Cruz says Senate Republicans likely have votes to confirm Trump Supreme Court nominee MORE questioned de Blasio on Thursday for joining the race.

“What should the rest of the country think when so many of your fellow New Yorkers are saying 'don’t run'?” Stephanopoulos asked.

De Blasio pointed to his reelection numbers, saying “the poll that actually matters is the election.”

“New Yorkers have twice said that they wanted me to lead them,” de Blasio said. “And I think about polling, in general, it’s not where you start, it’s where you end.”