Although Andrew M. Cuomo, the former governor, has not officially announced his candidacy for mayor of New York City, his prospective campaign received a significant boost on Saturday with an endorsement from H. Carl McCall, a prominent Black elder statesman and once a notable opponent of Mr. Cuomo.

In a public letter, Mr. McCall refrained from naming the current mayor, Eric Adams, but he expressed concern over a troubling sequence of events surrounding the Justice Department’s decision to dismiss federal corruption charges against Adams, which he argued raised doubts about the mayor’s autonomy from President Trump and highlighted the need for new leadership.

“New York deserves a representative whose loyalty to the city is unwavering,” Mr. McCall stated.

He added, “I have never formally encouraged anyone to run for office before, but this situation compels me to speak out. For these reasons, I wholeheartedly support Governor Andrew Cuomo and urge him to enter the race for mayor of New York City.”

The letter arrives as Mr. Cuomo, who stepped down from his position as governor amid scandal in 2021, is poised to take more definitive steps toward a comeback campaign for the mayoralty in the near future.

This endorsement further suggests that the previously strong bond between the city’s second Black mayor and the Black political community may be weakening, especially following allegations that the prosecutor handling the mayor’s case accused him of agreeing to a quid pro quo with officials from the Trump administration. On the same Saturday, Andrea Stewart-Cousins, the State Senate majority leader, also called for the mayor’s resignation, joining other Black leaders in their demands.