In her first trip to Turkey since the July 15 coup attempt, German Chancellor Angela Merkel received a lukewarm welcome from Turkish leaders. Unless Germany stops harboring criminals and supporting terrorism, she will be lucky to meet them at all next time around.In recent years, the Turkish-German relationship has been poisoned by Berlin's reckless actions. Having failed to stem the flow of foreign terrorist fighters to Syria, German authorities have allowed the PKK, which they themselves consider a terrorist group, to recruit, raise money and plan attacks within their borders. The already strained ties took another hit after the July 15 coup attempt in Turkey, as a number of high-profile Gülenist Terror Group (FETÖ) operatives tied to the bloody incident sought refuge in Germany.Although actions speak louder than words, Merkel desperately tried to appease a frustrated Turkish public in joint press conferences with President Recep Tayyip Erdoğan and Prime Minister Binali Yıldırım by paying lip service to the German-Turkish friendship and cooperation. At the Presidential Palace in Ankara, she was careful to list the PKK among terrorist organizations and pretended that her government was actually cracking down on the group at home. Hours later, the Turkish prime minister – out of diplomatic courtesy rather than genuine appreciation — thanked his German counterpart for supporting the Turks' war on terror.Theatrics aside, the Turkish-German relationship is heading for the rocks. Unless we publicly acknowledge that Germany is a state sponsor of terrorism and demand German authorities to take action or face the consequences, nothing is going to change.Today, PKK militants blow themselves up in urban areas and murder innocent people in cold blood. Under the circumstances, it's not possible for any government to treat them as freedom fighters or part of an insurgency. Having been openly backed by the U.S. in Syria and received tacit support from Germany and other EU members, the group has been emboldened in recent years.But their cooperation with German authorities goes back years. Everybody in Turkey knows that the PKK, along with other terrorist groups, have been operating freely on German soil under the condition that they do not engage in violence against German citizens. In order to appease the terrorists, Germany has repeatedly turned down requests by Turkish authorities for the extradition of known terrorists.To add insult to injury, Merkel reportedly asked Turkish leaders for concrete evidence linking FETÖ operatives in Germany to the July 15 coup attempt – which is something that she should be able to obtain with a phone call to the Federal Intelligence Service in Germany (BND). But her eagerness to harbor FETÖ terrorists should not come as a surprise. Germany was considered an attractive destination by FETÖ members precisely because Berlin had refused to comply with extradition requests in the past. In the end, Merkel ended up with more people with blood on their hands living among law-abiding German citizens. To make matters worse, the German-sponsored criminals and terrorists continue to live among more than 3 million Turkish taxpayers in the country – which doesn't just hurt Germany's relationship with Turkey but discredits Merkel's government in the eyes of the Turkish community.To be clear, Merkel can still save her country's relationship with Turkey and reverse the rise of right-wing extremism in Europe by engaging the Turkish leadership and reconsidering her stance on counterterrorism. Before the situation spins out of control, Europeans need to remember that the Turks protect them from the terror threat emanating from Syria.It is about time, Merkel, along with many of her European counterparts, should remember that they owe their political careers to the readmission deal signed with Turkey, which prevented the repeat of the 2015 refugee crisis, which was only created due to European intransigence and lack of compassion. European leaders should be taught that there is a price to pay for harboring terrorists that threaten Turkey's security.In order to make it clear that we mean business, Turkey should downgrade relations with Berlin and suspend military contracts along with bilateral trade agreements until Berlin reconsiders its stance on terrorism. At the same time, an additional question should be directed at Turkish citizens who will vote in the upcoming constitutional referendum: Do you support the annulment of the Turkey-EU readmission agreement?