President Trump wasted no time Thursday in attacking Mayor Bill de Blasio, slamming him as a “JOKE” after Hizzoner announced his run for the White House.

“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,” Trump tweeted shortly after 8:30 a.m.

“He is a JOKE, but if you like high taxes & crime, he’s your man. NYC HATES HIM!” he added about his fellow New Yorker.

While taxes may be sky high, the crime rate has actually gone down on de Blasio’s watch.

The mayor announced his candidacy before the president’s tweet with a three-minute YouTube video.

“Don’t back down in the face of the bully — take him on,” he says in the video. “As president, I will take on the wealthy, I will take on the big corporations, I will not rest until this government serves working people.”

He also vows to tackle Trump head-on.

“Donald Trump must be stopped. I’ve beaten him before and I’ll do it again,” de Blasio says.

During an appearance on “Good Morning America,” the mayor called the president “Con Don.”

“Every New Yorker knows he’s a con artist. We know his tricks. We know his playbook,” de Blasio said on the show. “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.”