ISTANBUL - Turks vote Sunday in the most-closely fought legislative elections since the Islamic-rooted ruling party came to power over a decade ago, in a crucial test for President Recep Tayyip Erdogan's plan for a new constitution to give him greater powers.
The election is taking place under the shadow of violence after two people were killed and dozens more wounded in an attack on a rally of the pro-Kurdish People's Democratic Party (HDP) in the southeastern city of Diyarbakir on Friday.
Opinion polls predict that the ruling Justice and Development Party (AKP) co-founded by Erdogan will again win the most votes, but its share could be sharply down on the almost 50 per cent it gained in the last such vote in 2011.
Turkey's economy is no longer firing on all cylinders, with growth slipping under three per cent and unemployment ticking up.
And concern is growing over the alleged authoritarian tendencies of Erdogan, who ruled as premier from 2003-2014 before taking on the post of president, with an upsurge in cases against journalists and other members of the public accused of insulting him.
Erdogan wants the AKP to win a two-thirds majority in seats, which would be enough to agree a new constitution to change Turkey from a parliamentary to a presidential system where the head of state is enshrined as number one.
He argues this would be little different from democracies like France and Brazil and change an old constitution that has its origins in the 1980 military coup. Opponents fear it could mark the start of one-man rule.
However the opposition HDP, expected to come fourth, could scuttle his plans if it wins over 10 per cent of the vote, which is Turkey's notoriously harsh threshold for sending MPs to parliament.
A strong showing from the second-ranked secular Republican People's Party (CHP) and third placed Nationalist Movement Party (MHP) could even force the AKP to form a coalition to stay in power for the first time since his first came to office in 2002.
The election campaign has been hugely divisive, with Erdogan lashing out at enemies in all directions, including several foreign media publications like Britain's The Guardian and the New York Times, which he told to "know your place".
He has also concentrated his most severe fire on the charismatic leader of the HDP, Selahattin Demirtas, belittling him as a "pretty boy" who is merely a front for Kurdistan Workers Party (PKK) separatist militants.
The attack on the HDP in Diyarbakir, caused by a bomb stuffed with ball bearings, was just the latest against the party in the campaign as it tries to break into the mainstream of Turkish politics.
"The aim was that chaos reigns in the country," Demirtas said at a rally in Istanbul Saturday, adding there had been 124 attacks against the party in the campaign.
Meanwhile, the CHP has sought to play on perceived excesses of the ruling party, even accusing Erdogan of having golden toilet seats in his new presidential palace in Ankara.
Erdogan's heavy involvement in the campaign is itself controversial, given as head of state he is required to keep an equal distance from all parties and he has made no secret of his favour for the AKP.
The AKP is now led by Prime Minister Ahmet Davutoglu, a bookish former foreign minister who has driven himself hoarse with a relentless campaign of populist speeches across the country to impress voters.
The party is seeking to convince the electorate with its hugely ambitious infrastructure projects, including a third airport for Istanbul and a multi-layer tunnel under the Bosphorus.
"The second half is beginning," says one of its main campaign slogans, implying another decade of ambitious projects.
Polls open at 0500 GMT and close at 1400 GMT with over 53.7 million Turks eligible to vote. Results are expected relatively quickly with a general picture emerging before the early morning.