In 1998, when Recep Tayyip Erdogan, then mayor of Istanbul, was sentenced to 10 months in jail for “inciting religious hatred” after he read out verses of Ottoman Islamist poet Ziya Gőkalp at a public event, many had written off his political future. The country’s Constitutional Court banned his Welfare Party on grounds that it was “threatening the Kemalist nature of Turkey, especially [its] secularity.” But what happened was just the contrary.

The jail term firmed up Mr. Erdogan’s resolve to fight Turkey’s secular establishment that had been backed by the powerful Army.

How did he rise to power?

Out of jail in 1999, he started mobilising supporters on an Islamist conservative agenda, and in two years, he co-founded the Justice and Development Party (AKP), the vehicle of his rise to power. Now, after the April 16 referendum victory, Mr. Erdogan, who spent 11 years as Prime Minister and is into the third year of his presidency, is in a position to overhaul the same Kemalist order which forced him to resign as Istanbul Mayor less than two decades ago.

What does it mean for Turkey?

The referendum was considered one of the most important events in modern Turkey’s history, by both supporters and opponents of Mr. Erdogan. It sought public approval for his ambitious plan to rewrite the Constitution and replace the current parliamentary system with an executive presidency. Parliament, dominated by Mr. Erdogan’s AKP, had already cleared the proposal. With 51.41% of the electorate voting Yes, the changes will kick in with the next presidential elections in 2019. The post of Prime Minister will be abolished.

The new President will have powers to appoint more than half the members of the nation’s highest judicial body, dissolve the national assembly, impose a state of emergency and rule through decrees.

The amendments will also guarantee two five-year terms for the President. In effect, Mr. Erdogan could rule Turkey till 2029 with expansive powers that no leader other than Mustafa Kemal Ataturk enjoyed.

Is he a dictator?

Supporters of the President say the constitutional changes are necessary for the progress and unity of an insecure Turkey. The referendum took place at a time Turkey is facing huge security challenges. There were multiple terror attacks last year, mostly by the Islamic State and a splinter group of the Kurdistan Workers Party (PKK). In the southeast, the Turkish military is waging a brutal war against the PKK and its affiliates. Mr. Erdogan’s claim is that only a strong leader could lead the country out of these challenges. But his critics fear that the constitutional changes would push Turkey towards dictatorship with so much power being concentrated in one person in a system that lacks the traditional checks and balances. The opposition says it is alarmed not just by Mr. Erdogan gaining more powers but by the overall changes in the system that could make the elected President is as powerful as a dictator. “It’s not a matter of Erdogan, it’s a matter of being against this systemic change,” says Bülent Tezcan, a lawmaker of the Opposition Republican Peoples’ Party.

How did he stem dissent?

What fuels concerns among Turkey’s democratic sections is the ongoing government crackdown on dissent. After last year’s failed coup attempt, for which Ankara blames Fethullah Gulen, a Turkish religious preacher living in the U.S., Mr. Erdogan went for a massive purge in government and private institutions, accusing tens of thousands of being supporters of the Gulenist network. Thousands have been arrested and sacked, including judges, academics and security personnel. Over 100 journalists are behind bars and 15 universities, 1,000 schools, 28 TV channels, 66 newspapers, 19 magazines, 36 radio stations, 26 publishing houses and five news agencies have been shut down.

The leading Kurdish Opposition politician is also in jail, while the country is still reeling under emergency. The Opposition questions the very legitimacy of the referendum that took place against this background. But Mr. Erdogan has won the referendum and he can now change the course of Turkish polity. However, given the deep polarisation in Turkish society that still has strong liberal currents despite the government’s excesses and the mounting security and economic challenges, he may not find it easy to run the country in unity even with his absolute powers.