Opinion polls show a result that will be close to that of June's general election, which failed to give any party an absolute majority, thanks largely to the rise in support for the left-wing, pro-Kurd People's Democratic Party (HDP).
In the ensuing months, Erdogan's Islamist Justice and Development Party (AKP), which had the largest share of the votes, failed to find a coalition partner, leading to this Sunday's rerun.
Since then the AKP has broken off peace talks with the Kurdistan Workers’ Party (PKK), bombed its positions and arrested thousands of alleged supporters.
The PKK responded with attacks on military targets, leading to shootouts in the streets of Diyarbakir and other towns in the Kurdish-majority east, although it recently declared a unilateral ceasefire.
And suicide attacks on two pro-peace rallies have claimed some 200 lives.
They were the work of the Islamic State armed group (IS) fighting in Syria and Iraq but the HDP has accused the government of facilitating the carnage, despite the fact that it is supposed to be helping the West fight IS.
The resumption of hostilities with the PKK has seen the outlines of a new alliance emerge between the AKP and right-wing nationalists in politics and the military.
The hard-right, secular Nationalist Action Party (MHP) joined the more left-wing Republican People’s Party (CHP) in accusing Erdogan of undermining the secular nature of modern Turkey and of becoming increasingly autocratic.
But its armed wing, the Grey Wolves, is alleged to have cooperated with AKP members in attacks on HDP offices and left-wingers suspected of sympathy for the Kurds.
And elements of the “deep state” – secretive elements in the security forces, working with criminal elements, that have plotted coups and carried out bombings and murders in the past – are believed to be cooperating with their Islamist former enemies in the violence.
Recent months have also seen attacks on journalists - a former BBC producer was recently found dead in an Istnabul airport - and the offices of newspapers critical of the AKP and legal action against people, including a 17-year-old boy, for publishing remarks deemed disrespectful of the president.
The turbulence could frighten some voters into backing the strongman Erdogan.
Or it could lead to the declaration of a state of emergency and the election being called off.
But it could also mean that, if the election goes ahead and the HDP wins more than the 10 per cent it needs to have MPs, the AKP will try to form an “Islamo-nationalist” government with the MHP.
There could also be splits in the AKP with some members, including former president and Erdogan ally Abdullah Gul, reportedly thinking of forming their own party because of what they see as the president’s autocratic and aggressive tendencies.
Whatever government is formed would rule a deeply divided Turkey, facing a revived war with the PKK and fallout from the bloody Syrian conflict.