President Erdogan was never going to take the loss of Istanbul lying down. "Whoever wins Istanbul wins Turkey", he has often said. He is determined to win back the country's economic powerhouse.
But it's a strategy fraught with risk. The Turkish lira - which has lost more than 30% over the past year - has slumped again. An economy in recession can hardly cope with more uncertainty. After all, it was economic woes that lost Istanbul for Mr Erdogan in the first place.
What's more, Ekrem Imamoglu, who was formally appointed mayor last month, is gaining popularity, fast. He's reached out beyond his base and has settled into the role with ease. The rerun could widen his win - barring major irregularities against him, which many of his supporters fear.
And Mr Erdogan's own party is deeply split on the issue. His diehard loyalists believe victory was stolen. But other wings of the party accept they lost, and that rejecting the result is another nail in the coffin for what's left of Turkish democracy.