ISTANBUL — Engin Bayrak owns a hardware store near the shores of the Golden Horn waterway, where ferries connect the European and Asian sides of this vast city. He has witnessed for himself the vast improvements in services over the last decade as Prime Minister Recep Tayyip Erdogan and his Islamist-rooted Justice and Development Party reshaped this city in their image.

“Clean water, reliable electricity — things we take for granted now — we didn’t have this before,” Mr. Bayrak said.

Even so, he says, now that a corruption scandal has exposed the dark side of the city’s steady growth, he will no longer support Mr. Erdogan or his party, known by the initials of its name in Turkish, A.K.P., in coming elections.

“It’s what came after this that has ruined this city,” he said. “The crazy projects are not crazy, they are greedy projects. While we got a few basic amenities, the government and Erdogan got rich. They built an empire on our land, without asking for our permission.”