By the end of May 8, the roster was complete.

People in Turkey had until 8pm local time to gather the 100,000 signatures that independent candidates need to run for president in the upcoming snap election.

One woman and five men will be on the ballot on June 24. That makes it—on paper, at least—the most competitive presidential election yet.

But Turkish election campaigns have long been fought on an uneven playing field.

Successive reports by OSCE monitors have documented how Turkey’s governing Justice and Development Party (AKP) has repeatedly used its grip on newspapers and broadcasters and its control of state institutions to pass its message to Turkish voters at the opposition’s expense.

This election will be the most uneven yet and that is because of the plight of the Peoples’ Democratic Party (HDP), a left-wing outfit that is the most successful Kurdish political movement Turkey has ever seen.

The party confounded expectations by emerging from the last election three years ago as the third-largest in parliament. Since then, however, its influence has dwindled: amid accusations of collusion with the PKK, a Kurdish militant group that Turkey considers a terrorist organisation, parliament waived HDP MPs’ immunity from criminal prosecution and allowed the police to swoop in.

Nearly all of the party’s 59 members of parliament have been arrested, charged or sentenced to lengthy prison terms. By one measure, just eight of its MPs have not spent at least some time in police custody since they were elected in 2015.

One former leader, Selahattin Demirtas, was the HDP’s candidate for president in 2014 and is standing this time too. But a stuttering trial – on charges of glorifying terrorism, among others – has kept him behind bars for 18 months. He won’t be released to join the election campaign.

Despite the gloom, Turkey’s Kurdish population remains a potent electoral force – especially in the southeast of the country, in those districts that are closer to Iraq and Syria than Ankara and Istanbul.

This will be one of the most important battlegrounds in the parliamentary election, which takes place alongside the presidential one on June 24.

Last week four Turkish opposition parties decided to work together in their efforts to unseat President Recep Tayyip Erdogan’s party by forming an electoral alliance. The decision was an unprecedented attempt to overcome their notorious divisions – but it was also incomplete because the HDP was excluded.

This is an electoral force for richer, more populous provinces in western Turkey. None in the new opposition alliance are likely to make much of a showing in the southeast.

In the 14 provinces that make up this part of Turkey, the election will be a two-horse race between the political left, represented by the HDP, and the social conservatism of the AKP. Both can appeal to vast numbers of Kurdish voters.

But this will not be a straight contest because of a serial gremlin in election rules: the threshold.

The law says that any party hoping to elect MPs to parliament must first secure 10 percent of valid votes cast nationwide (unless they are in a registered formal alliance with more successful parties on the ticket). Thresholds are a commonly-used tool to discourage fragmentation and keep broad alliances together, but Turkey’s is one of the highest in the world and benefits big parties at the expense of the small.

Take Diyarbakır, the large and overwhelmingly Kurdish city in southeast Turkey, which next month will elect 12 members to the 600-seat parliament.

At the last election the HDP won nearly three quarters (71%) of all votes cast, a clear landslide. The AKP was its closest challenger on 22%. Other parties competed, but none scored more than a single percentage point.

Turkey’s proportional system meant the AKP was given two seats in the city while the HDP took the rest.

But if the Kurdish party had failed to cross the national vote threshold at the last election, all of the seats would have gone to the AKP.

The concern this time is that the HDP’s hardships could lead to it falling just short of the 10% threshold.

It would exclude a major political force representing Turkey’s largest ethnic minority from parliament.

But it would also gift 79 seats directly to the AKP, the only other competitive party in the region, at a time when an opposition alliance is directly challenging its dominance in the west of the country.

There is talk of an informal pact between the HDP and the opposition’s alliance, where other parties will put up only symbolic candidates and implicitly encourage tactical voting against the AKP in the southeast.

But such a deal would still pit the HDP against other opposition parties in more westerly cities – Istanbul, Ankara, Izmir and Adana included – where they won votes and seats aplenty last time.

In short, this is the riskiest election yet for Turkey’s Kurdish party. Falling short of the threshold by even a few thousand votes could allow Erdogan to retain the parliamentary majority he seeks.