Germany's increasingly strained ties with Turkey took center stage during Sunday's televised debate between German Chancellor Angela Merkel and her main competitor in the September 24 elections, Martin Schulz.

Merkel said that given deteriorating relations and worrying developments in Turkish democracy, "it is clear that Turkey should not become a member of the European Union."

Merkel was responding to an even stronger debate claim from Schulz, who had said that he would move to formally halt Turkey's EU membership talks if he were elected chancellor.

Merkel stopped short of endorsing formally ending Turkey's EU accession talks because, she said, they were already effectively frozen and because it was important to maintain dialogue.  But she added that she didn't "see [Turkey] ever joining and I had never believed that it would happen."

Instead, the chancellor said she supported imposing economic penalties on Ankara and blocking talks on expanding Turkey's customs union agreement with the EU, a move with severe potential repercussions for Turkish exporters.

The German politicians' comments drew sharp criticism from Turkish officials, with the country's Foreign Minister Mevlut Cavusoglu saying that Europe "was turning to the values of the pre-Second World War era...savagery, fascisim, violence, intolerance."

Turkey's EU Minister Omer Celik Merkel and Schulz of using "careless" and "disrespectful" language against Turkey. 

President Recep Tayyip Erdogan's spokesman, Ibrahim Kalin, said on Twitter that the debate showed how Germany's top politicians were succumbing to "populism and exclusion." 

Here is a look at Turkey's EU accession talks and where they stand.

Morbid EU accession talks

In 1987, Turkey applied to join the European Economic Community, the predecessor to the EU. It was formally accepted as an EU candidate country in December 1999. Negotiation for membership did not start until 2005, after Cyprus had become a fully-fledged EU member.

Turkey's EU accession talks have effectively been stalled for years due backtracking of reforms and the deterioration in the rule of law.

Massive purges in the wake of the July 2016 failed coup attempt and a constitutional referendum in April this year granting President Recep Tayyip Erdogan sweeping powers have added to calls to formally end Turkey's EU accession bid.

In response to the purges under an ongoing state of emergency, the EU said in December last year that it would open no new chapters for Turkey's membership. This was followed in July by the European Parliament in a non-binding vote calling for the suspension of Turkey's EU membership talks.

The EU's so-called accession chapters are areas of negotiations every EU candidate country must pass to bring its laws and regulations in line with the bloc. Turkey has only 16 of 31 chapters open. Ankara has only provisionally closed one chapter. Many of the most troublesome issues remain unopened, with no progress made in the 12 years of formal talks.

The stalled EU membership talks come despite the EU last year promising to open new chapters at an "accelerated pace" as part of a deal with Ankara to stem migrant flows.

European Commission President Jean-Claude Juncker said last week that he suspected Turkey wanted Brussels to break off the accession talks, so that Ankara could "blame the European Union" for their failure.

Today's situation in Turkey is a far cry from heady expectations when Erdogan, who was prime minister up until 2014, and his AK Party came to power in 2002 on a pro-EU platform that promised greater rights, freedom and prosperity.

The hope in European capitals at the time was that the EU process would anchor to Turkey to the West and cement democracy.

Privileged partnership

While Merkel made sharp comments on Turkey in the debate, her opposition to full membership is not new. In 2004, Merkel and her conservatives had advocated a policy of "privileged partnership," an alternative to full membership for Turkey.

The idea was that Ankara and the EU could find multiple areas to cooperate, but full membership (including free movement of labor) of a country of 80 million people bordering on the instability of the Middle East would strain the EU's capacities.

Turkey has long been opposed to the privileged partnership idea.

Customs Union

Merkel's comments on halting Customs Union expansion talks are likely to have the most bite. Turkey joined the EU Customs Union in 2005, paving the way for the bloc to be Turkey's largest trading partner, accounting for 40 percent of the country's trade.

However, the Customs Union doesn't include agriculture, services and government procurement. One study found that an expanded Customs Union could lead to a nearly 2 percent increase in Turkish GDP growth, 95 percent increase in agricultural exports and a 430 percent increase in service exports. 

A new customs union agreement also promised to address Turkey's longtime complaint that countries with free trade agreements with the EU are allowed to access the Turkish market tariff free without reciprocation for Turkish goods.