The upholding last week of a legal challenge to the outcome of Istanbul’s mayoral election has paved the way for a divisive new contest. It will inevitably lead to a confrontation between Turkey’s most powerful political figure, president Recep Tayyip Erdoğan and the surprisingly able Ekrem İmamoğlu, the candidate of the opposition alliance who won the race to be mayor of Istanbul.

On 31 March, local elections across Turkey saw the resurgence of opposition to Erdoğan’s Justice and Development party (AKP), which lost control of the municipal government in the capital Ankara – as well as losing the mayoral race in Istanbul, the president’s home town.

İmamoğlu originally defeated Erdoğan’s candidate and former prime minister Binali Yıldırım – only to see his victory revoked by Turkey’s high electoral board on grounds that the setup of some of the ballot box committees was in contravention of electoral law. New mayoral elections are now to be held on 23 June. The board’s decision was heavily criticised by Turkey’s opposition for being politically motivated and lacking legal justification.

There were four votes in March in Istanbul – for metropolitan mayor, as well as three other campaigns for district mayors, the municipal council and neighbourhood administrators. Despite all four ballots being placed in a single envelope and counted in the same manner, the board has only annulled the votes cast for metropolitan mayor. The board said it could only rule on complaints it receives from political parties, and the challenge lodged by the ruling alliance was for the metropolitan race only: AKP officials made complaints over unsigned results documents and said that some ballot box officials were not civil servants. Previously, the board has been very inconsistent on how it upholds such complaints – especially when they come from opposition parties.

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Crucially, the board has not publicly disclosed the results of its electoral impact analysis. To rule for an annulment, the board is required to demonstrate that the alleged violations were consequential enough to impact the outcome of the election. Such proof has yet to be shared with voters.

Nonetheless, the board has set the stage for a re-run of the Istanbul election in six weeks’ time. The outcome will be shaped by four factors: victimisation, mobilisation, consolidation and economics.

The ruling has created an opening for a narrative of victimisation that will be used by both sides to galvanise their grassroots supporters. For the ruling AKP, the victimisation stems from their claims that the opposition cheated to win in March. The message will be that AKP voters should use the new vote to redress this affront to democracy.

The opposition will also consider themselves victims. March’s triumphant mayor, İmamoğlu will claim that his victory was stolen by an electoral board operating under political pressure.

The candidates will also seek to consolidate the support they received on the 31 March. The key here will be the Kurdish vote, which tended to back the opposition candidate. İmamoğlu will need to call on this support again, while the AKP will try to attract voters by signalling a future softening of government policy on Kurdish issues. The challenge for Erdoğan will be to find a policy shift that would get traction with pro-Kurdish voters in Istanbul while avoiding a backlash among his Turkish nationalist support nationwide.

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The result of the March elections were seen as a judgment on Erdoğan’s handling of the economic crisis in Turkey – the country’s first recession since he took national power 16 years ago. The volatile economy and the risks of a US-China trade war could raise further frustrations and fuel the protest vote against Erdoğan’s candidate.

Recognising these risks, Erdoğan has decided to be fully involved in the elections for Istanbul. He recently announced that he will stage more than 30 rallies before election day on 23 June. For the first time in the history of the country, the president is pitting himself against a local candidate. That is how important the race in Istanbul has become – and it may be a glimpse of how Turkey’s future confrontations over executive power could play out.

• Sinan Ülgen is the executive chairman of the Istanbul-based EDAM thinktank and a visiting scholar at Carnegie Europe