To many in the Ukrainian Black Sea port city, Mayor Gennadiy Trukhanov embodied the old, corrupt politics — with his history of suspected criminal links and corruption cases and a political past tied to a pro-Kremlin party. In ousting him, Mr. Zelensky accused him of holding Russian citizenship.

Yet the mayor’s downfall has mostly brought concern, even among local opponents who had long wished him gone. Many residents said the evidence behind the accusation of holding Russian citizenship looked fabricated, prompting concerns that it was part of a broader power grab by the president to remove a political rival.

Mr. Zelensky had moved swiftly. He revoked Mr. Trukhanov’s Ukrainian citizenship, forcing him out of office, and then installed a military administrator to run Odesa alongside an acting mayor — the City Council’s secretary, a member of Mr. Zelensky’s party.

“I can’t feel happiness,” said Oleksandra Kovalchuk, who ran on Mr. Zelensky’s party list in the last municipal elections. “Not under these circumstances.”