ANKARA, Turkey (AP) — In the year in which the Turkish republic marks its centenary, the country is being closely watched to see if a united opposition can succeed in unseating an increasingly authoritarian leader in the NATO-member country.

Turkey’s presidential and parliamentary elections, taking place on Sunday, could stretch President Recep Tayyip Erdogan’s rule into a third decade — or they could set the country on a new course.

Kemal Kilicdaroglu, the leader of the secular, center-left Republican People’s Party, or CHP, is the main challenger trying to dislodge Erdogan after 20 years in office. The 74-year-old is the joint candidate of a six-party alliance that has vowed to dismantle an executive presidential system that Erdogan installed and return the country to a parliamentary democracy with checks and balances.

As well as the opposition alliance, Kilicdaroglu has clinched the support of the country’s pro-Kurdish party, which garners around 10% of the votes. And polls have given him a slight lead. The race is so close, however, that it is likely to be decided in a runoff between the two frontrunners on May 28.

Erdogan, has lost some ground amid a faltering economy and a cost-of-living crisis. His government has also been criticized for its poor response following a devastating earthquake that struck southern Turkey and killed tens of thousands earlier in the year.

“For the first time in the 20 years since Erdogan came to power, he’s facing a real electoral challenge which he may actually lose,” said Ozgur Unluhisarcikli, director of the German Marshall Fund’s Ankara office, adding that the race was about two competing visions.

“On the one hand, there is President Erdogan’s vision of a security state, a monist society, of power consolidated in the hands of the executive,” he said. “On the other hand, there is the vision, represented by Kilicdaroglu, of a more pluralist Turkey in which no community is othered, one that is getting more democratized and ... there’s a clear division of powers between the executive, legislative and judiciary.”

Erdogan is vying for a third presidential term, having served three terms as prime minister before that. The 69-year-old leader of the conservative and religious Justice and Development Party, or AKP, is already the country’s longest serving leader. A highly divisive politician, Erdogan has based his electoral campaign on past achievements, presenting himself as the only politician who can rebuild lives following the Feb. 6 earthquake in southern Turkey that leveled cities and killed over 50,000 people.

He has also embarked on a spending spree ahead of the elections, including increasing the minimum wage and pensions, in a bid to offset the effects of inflation.

During his campaign stops, Erdogan has tried to portray the opposition as colluding with “terrorists” as well as with foreign powers wanting to harm Turkey. In a bid to consolidate his conservative base, he has also accused the opposition of supporting “deviant” LGBTQ rights and of being “drunkards.” On Sunday, hundreds of thousands of his supporters were shown a faked video depicting a commander of the outlawed Kurdistan Workers' Party, or PKK, singing an opposition campaign song.

Kilicdaroglu, meanwhile, is a soft-spoken politician who is credited with bringing a previously fractured opposition together. His six-party Nation Alliance, that includes Islamists and nationalists, has vowed to reverse the democratic backsliding and crackdowns on free speech and dissent under Erdogan.

Two other candidates are also in the race for the presidential post but are considered outsiders. They are Muharrem Ince a former CHP leader who lost the last presidential election to Erdogan in 2018, and Sinan Ogan, a former academic who has the backing of an anti-immigrant nationalist party. Ince, who heads the Homeland Party, has come under criticism from Kilicdaroglu supporters who accuse him of splitting the votes and forcing the elections into a runoff.

The main issue for the elections is the economy and high inflation that has eaten away families' purchasing power.

In Istanbul, tea-shop owner Cengiz Yel said he would vote “for change” because of the government's mishandling of the economy.

“We worry about the rent, the electricity, and other bills.” Yel said. “For the past year, I have been starting each new month with more debt.”

Others profess their enduring love for a leader who improved infrastructure in the country and lifted many out of poverty in the early years of his rule.

“I love my nation. I want to be with a leader who serves his nation," said Arif Portakal, a 65-year-old Erdogan supporter in Istanbul.

The campaign has been marred by some violence. On Sunday, protesters in the eastern city of Erzurum hurled rocks as Istanbul’s mayor, Ekrem Imamoglu, was campaigning on Kilicdaroglu’s behalf from the top of a bus. At least seven people were hurt.

Voters will also cast votes to fill seats in the 600-member parliament. The opposition would need at least a majority to be able to enact some of the democratic reforms it has promised.

More than 64 million people, including 3.2 million expatriate Turkish citizens, are eligible to vote. More than 1.6 million people have already voted in ballots overseas or at airports. Voter turnout in Turkey is traditionally high.

There are concerns over how voters among the 3 million people who have been displaced following the earthquake that devastated 11 provinces will be able to vote. Officials say only 133,000 people who were forced to leave their hometowns have registered to vote at their new locations. Some political parties and nongovernmental organizations plan to transport evacuees back to the earthquake zone to allow them to vote.

Many have questioned whether Erdogan would accept an electoral defeat.

In 2015, Erdogan is believed to have worked behind the scenes to block coalition talks after his ruling party lost its parliamentary majority in elections. The party regained a majority in repeat elections a few months later. And in 2019, the ruling party challenged the results of local elections in Istanbul after the AKP lost the mayoral seat. That time, however, the party suffered a more humiliating defeat in the repeat election.

Observers are keen to see whether an organized opposition can overcome the hurdles in a country where the leader exerts strong control over the media, the judiciary and the electoral body, and nevertheless achieve a peaceful change of regime.

“The world is watching because this is also an experiment, because Turkey, like some other countries, has been going down the authoritarian path for a while,” said Unluhisarcikli. “And if this trajectory can be reversed through elections only, that could set an example for other countries.”

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Mehmet Guzel contributed from Istanbul.