Jeffries, who represents parts of Brooklyn, said in a statement he gave first to The New York Times that while he and Mamdani had "areas of principled disagreement," he acknowledged the state assemblyman's win in the June primary and called for unity.
"Zohran Mamdani has relentlessly focused on addressing the affordability crisis and explicitly committed to being a Mayor for all New Yorkers, including those who do not support his candidacy," Jeffries said. "Together, along with Mark Levine and Jumaane Williams, they won the nominations for Mayor, Comptroller and Public Advocate in a free and fair election. In that spirit, I support him and the entire citywide Democratic ticket in the general election."
Jeffries said as with any mayor, there will be areas of disagreement, yet the "stakes are existential."
"In this environment, we have a clear obligation to push back against the national nightmare being visited on the American people by Republican extremism. Donald Trump must be given no space to haunt the people of New York City," Jeffries said. "I endorse the Democratic ticket."
During a news conference at the Capitol on Friday morning, Jeffries pointedly clarified that he has "not refused" to endorse the Democratic nominee for mayor.
"I have not refused to endorse. I refused to articulate my position, and I will momentarily, at some point in advance of early voting," Jeffries said Friday morning.
Mamdani didn't take any questions about Jeffries during a news conference outside a Bronx mosque on Friday afternoon, but released the following statement after the endorsement:
"This campaign has always been about bringing people together to improve the quality of life for every New Yorker," the statement said. "I welcome Leader Jeffries' support and look forward to delivering a city government and building a Democratic Party relentlessly committed to our affordability agenda - and to fighting Trump's authoritarianism. Our movement to turn the page on the politics of big money and small ideas grows stronger by the day."
During the press conference outside the mosque, Mamdani condemned his opponents for what he described as Islamophobic rhetoric.
"For as long as we have lived, we have known that no matter what anyone says, there are still certain forms of hate that are acceptable in the city. Islamophobia is not seen as inexcusable," Mamdani said.
Mamdani blames Andrew Cuomo for an appearance on WABC Radio, where the former governor told conservative radio host Sid Rosenberg that Mamdani was not qualified to handle a crisis, like a second 9/11.
"He'd be cheering," Rosenberg said.
But Cuomo did not push back and appeared to laugh. Mamdani blamed Mayor Eric Adams for comments he made Thursday and Republican Curtis Sliwa for comments he made at Wednesday's debate.
"Eric Adams said that we can't let our city become Europe. He compared me to violent extremists," Mamdani said. "And he lied again and again when he said that our movement seeks to burn churches and destroy communities. The day before that, Curtis Sliwa slandered me from the debate stage when he claimed that I support global jihad."
Later Friday, Cuomo hugged several Jackson Heights imams before accusing Mamdani of dividing New Yorkers and playing the victim.
"Today he is playing the victim but in reality he is the offender," Cuomo said. "What he is doing is the oldest dirtiest political trick in the book. Divide people."
Cuomo said he didn't take the comment Rosenberg made about 9/11 seriously.
"I didn't take it seriously, of course I think its offensive comment, period," Cuomo said. "But it did not come out of my mouth. That the point."
The radio host took full responsibility on Friday, posting in part: "Leave Cuomo out of it."
Early voting begins Saturday morning in New York.
(ABC News contributed to this report.)
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