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 hammered 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 (D) Thursday shortly after the mayor announced his presidential bid, slamming his fellow New Yorker as a “JOKE.”

“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!” Trump tweeted.

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

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De Blasio launched his White House bid Thursday with a vow to help the working class and a harsh rebuke of the president.

“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.”

De Blasio has emerged as a vocal critic of Trump, holding a news conference on Monday in Trump Tower where he promoted new regulations curbing energy use by the city’s buildings. He added that 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 later got into a heated Twitter exchange 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, who became the 24th contender to throw his hat into the ring for the Democratic presidential nomination, faces an uphill battle against more established progressives who have been campaigning and raking in donations for months. The New York mayor could also initially struggle to raise the necessary funds to land a spot on the primary debate stage next month.

He could also face hometown opposition, as 76 percent of New York City residents said in a Quinnipiac University poll released last month that he should not run for president.

Updated at 9:02 a.m.