ISTANBUL -- Millions of voters in Istanbul go back to the polls for a controversial mayoral election re-run Sunday, as President Recep Tayyip Erdogan's party tries to wrest back control of Turkey's largest city.
The high-profile vote is taking place because Turkey's top election authority ruled in favor of Erdogan's Justice and Development Party, AKP, and canceled the result of the March 31 vote for mayor of Istanbul, which had given a narrow victory to opposition candidate Ekrem Imamoglu. The decision cited a breach of laws concerning the composition of officials overseeing the vote.
The controversial decision fueled concerns over democracy and the rule of law in Turkey, a NATO member that is still formally a candidate to join the European Union. Turkey is also a key Western ally in the fight against terrorism and in stemming the flow of refugees to Europe.
The race for Istanbul is seen as a test of Erdogan's popularity amid a sharp economic downturn, rising unemployment and high food prices. To its critics, the Islamic-based AKP is entering the election with its democratic credentials dented for triggering the repeat vote.
The election is important because the city of 15 million, straddling Europe and Asia, is Turkey's financial, commercial and cultural center, with a budget worth $8.8 billion last year.
"It's very risky for any political party to lose Istanbul," said Can Selcuki, general manager of the Istanbul Economics Research think tank. "The budget of Istanbul is larger than some sovereign GDPs of small countries."
The loss of Istanbul in March was a blow to Erdogan's 25-year dominance of the city as mayor and backer. He was born in the city and began his political career as mayor. He once famously said: "Whoever wins Istanbul wins the whole of Turkey."
Erdogan has dominated Turkish politics for the past 16 years, but a loss could put him on shaky political ground. News media reports suggest there is growing dissent within his party, with former party heavyweights including ex-President Abdullah Gul and former prime minister Ahmet Davutoglu reportedly preparing to launch breakaway parties. The two men have openly criticized AKP for seeking a redo of the Istanbul vote.
"The rerun decision ... definitely made the cracks within the AKP more visible," Selcuki said. "If Mr. Imamoglu wins, it's likely those cracks will become even more visible."
Opinion polls suggest Imamoglu, of the secular center-left Republican People's Party, has a slight lead over his rival, the AKP's candidate Binali Yildirim, who is a former prime minister, transport minister and parliament speaker.
Imamoglu, who was mayor for just 18 days before his win was canceled, has cast the election as a battle for democracy, insisting his victory was unfairly seized.
In an interview with The Associated Press earlier this week, Imamoglu said he believes the "injustice" caused by the cancellation will galvanize voters in his favor.
"I believe the people of Istanbul will give the necessary response to this injustice at the polls as a result of their belief in democracy," Imamoglu said.
A relative newcomer, the former mayor of Istanbul's suburban Beylikduzu district has promised to end divisions in the politically polarized city. Openly religious, he is vying for votes from the AKP's traditional base.
Despite the conciliatory language, he has also vowed to expose excessive spending by the AKP-run municipality and promises to end corruption.
Before the March vote across Turkey, Erdogan had led the AKP campaign to shore up nationalist and religious sentiment, framing the elections as part of a fight to safeguard the nation three years after a failed coup attempt.
He has taken a backseat for most of the re-run campaign, but returned to the spotlight in the late stages to attack Imamoglu, accusing him of "acting together with the terror organization," in reference to outlawed Kurdish rebels.
Yildirim has touted his track record as transport minister, highlighting the completion of major projects that include a third bridge over the Bosphorus and a new airport for the city.
The party has been targeting AKP voters who abstained on March 31 — apparently to punish it for last year's currency crisis that triggered high inflation and food prices to soar.
"The air is good. ... The political air is good and the result will be very good," he told the AP while taking a short break from campaigning.
Mehmet Guzel and Zeynep Bilginsoy in Istanbul contributed.