New York Assemblyman Zohran Mamdani, who is on track to win the Democratic Party ’s nomination in the New York City mayoral race, on Wednesday reacted to Donald Trump calling him a “100% Communist Lunatic” following his surprise success, warning the president that he is prepared to challenge the more cruel elements of his agenda.

Ackman said he was “gravely concerned” because he believed the left-wing candidate’s policies would be disastrous, triggering an exodus of the wealthy that would endanger New York’s public services by hollowing out its tax base.

Sen. Chuck Schumer and Rep. Hakeem Jeffries, New York City natives who lead their parties’ caucuses in each chamber of Congress, quickly issued statements saying they had spoken to Mamdani and praising the campaign he ran. They stopped short of endorsing him.