Millions of Turkish citizens will vote in a referendum on Sunday that will decide whether to replace the country's existing parliamentary system with a presidential system. A "yes" vote would mean the biggest change in Turkey's mode of governance since the modern Turkish republic was founded on the ashes of the Ottoman Empire almost a century ago.
A "yes" vote will hand wide-ranging executive powers to the presidency. The post of prime minister would be abolished and the president will be able to retain ties to a political party.
President Recep Tayyip Erdogan has campaigned for a "yes" vote. But on Friday he ruled out any fundamental changes to the republic if the "Yes" campaign wins.
"In my 40 years of political life, I have had no such claims to change the regime," Erdogan said.
He said that debate ended in 1923, when Mustafa Kemal Ataturk established modern Turkey as a republic.
Polls indicate that the campaign has split the country of 80 million roughly down the middle, its divisions spilling over to the large Turkish diaspora abroad.
Erdogan's supporters see the president as a leader who allowed greater religious freedoms back into Turkey's public life, championed the pious working classes and delivered airports, hospitals and schools.
"Within the past 15 years he has achieved everything once considered impossible, unthinkable for Turks, be it bridges, undersea tunnels, roads, airports," said Ergin Kulunk, 65, a civil engineer who heads an association that is financing a new mosque in Istanbul.
"The biggest quality of the Chief [Erdogan] is that he touches people. I saw him at a recent gathering literally shaking almost 1,000 hands. He's not doing that for politics. It comes from the heart," he said.
Opponents fear a shift towards a stronger presidency chips away at the secular foundations laid by Ataturk.
"He's trying to destroy the republic and the legacy of Ataturk," said Nurten Kayacan, 61, a housewife from the Aegean coastal city of Izmir, attending a small "No" rally at an Istanbul ferry port.
"If the "yes" vote wins, we're headed to chaos. He will be the president of only half of the country," she said.
A close vote
Erdogan assumed the presidency, then a largely ceremonial position, in 2014 after more than a decade as prime minister.
He led opposition to a failed coup in July 2016 and has since argued that strong leadership is needed to defeat Daesh, the PKK and the Gulenist movement in Turkey, which the government accuses of masterminding the failed putsch.
A poll two weeks after the attempted putsch showed him with two-thirds approval, his highest ever, but more recent surveys suggest a much closer race. A narrow majority of Turkish citizens will vote "yes," two opinion polls suggested on Thursday, with "yes" polling just above 51 percent.
Erdogan believes the "yes" vote could be bigger than that. "Some predict the rate to be below 55 percent while others say it is likely to be between 55 to 60 percent," he said on Friday.
Pollsters acknowledge there may be a hidden "no" vote, following the failed coup and concern at the scope of the crackdown in its wake.
Erdogan's supporters reject such charges. They say the 18 constitutional amendments being put to a simple "yes/no" vote contain sufficient checks and balances, such as the provision that a new presidential election would be triggered should the president dissolve parliament.
The outcome will also have repercussions beyond Turkish shores.
Never in recent times has Turkey, one of only two Muslim members of the NATO military alliance, been so central to world affairs, from the fight against Daesh in Syria and Iraq, to Europe's migrant crisis and Ankara's shifting allegiances with Moscow and Washington DC.