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) again feuded with 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 Friday, referring to the president as "Con Don" and calling him "very low energy."

De Blasio launched his presidential campaign on Thursday with sharp words against fellow New Yorker Trump, with whom he has frequently feuded as mayor.

"In the course of this campaign, we’re going to talk about what working people need and how their government should be on their side. 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. I call him 'Con Don,'" de Blasio said during an appearance on ABC's Good Morning America on Thursday, soon after launching his campaign.

ADVERTISEMENT

It didn’t take long for Trump to respond. Hours later, he fired back in a video posted on Twitter, saying de Blasio is a "joke" while also calling him "the worst Mayor in the history of New York City."

.@BilldeBlasio is the worst Mayor in the history of New York City - he won’t last long! pic.twitter.com/NyYntsX573 — Donald J. Trump (@realDonaldTrump) May 16, 2019

De Blasio kept up his own insults against Trump on Friday, during an appearance on MSNBC's "Morning Joe."

“Con Don himself not only tweeted at me, he created his own video,” de Blasio cracked. “I was very impressed."

De Blasio also called Trump “very low energy” and a “bully.”

Trump has frequently used insulting nicknames against his rivals, including calling former Florida Gov. Jeb Bush "low energy" during the 2016 Republican primary.

“There’s nothing about Donald Trump that surprises me, there’s nothing about him that intimidates me,” de Blasio said on "Morning Joe."

“If you’re going to take on Donald Trump, it sure helps to be able to fight back and understand how to deal with him,” de Blasio said.

“I think it’s about knowing how to take on the bully,” de Blasio said. “Go right at him and take him down.”