On the eve of New York City’s mayoral election, President Trump was seen threatening Zohran Mamdani that if he won, Trump would only allow the city to get the bare minimum when it came down to federal funding.
Sources are now speaking about how illegal that really is and if he possesses the legal authority to cut or deny funds to the city in such a situation.

Under the US Constitution, Congress controls federal appropriations. Congress has full power to collect taxes and spend for national requirements. As per Section 9, no money shall be drawn from the Treasury but in Consequence of Appropriations made by law.
The Impoundment Control Act of 1974 limits any president’s power to withhold funds that have already been appropriated by Congress. Under such an act, the president could delay payments for nearly 45 days, but it would further require approval from Congress.

The Constitutional lawyer further quoted in that piece that the president cannot legally defund a city until Congress has explicitly conditioned the funding, and in such a condition, it’s tied to the sole purpose of those funds.
So, despite all the threats that he’s made, Trump cannot legally withhold or reduce federal funds to NYC.