U.S. Secretary of State, Mike Pompeo, and Turkish Foreign Minister, Mevlüt Çavuşoğlu, agreed at a meeting in Singapore on Friday to work on resolving a number of disputes that have disrupted the two countries’ relationship recently.

The main dispute that has caused tensions to escalate between the NATO allies is Turkey’s detention of Andrew Brunson, a U.S. citizen who was arrested without probable cause almost two years ago.

Brunson, who is originally from North Carolina, is an evangelical pastor who has lived in Turkey for over two decades with his wife and three children. Before his arrest, he worked as a pastor at the small Izmir Resurrection Church, where he led a congregation of around two dozen people, according to the BBC.

In 2016, Brunson was arrested by Turkish authorities in a brutal crackdown that took place after a failed military coup that took place in July of that year. Brunson was one of thousands of people arrested, including journalists, activists, and opponents of Turkish President Recep Tayyip Erdoğan.

The evangelical pastor was arrested in October 2016 for allegedly being a spy and supporting the outlawed Kurdistan Workers’ Party (PKK). Brunson was also suspected of supporting U.S.-based cleric, Fethullah Gülen, who the Turkish authorities accuse of planning the failed 2016 coup attempt that claimed 250 lives.

After spending 21 months in a Turkish prison, Brunson was transferred to house arrest last week. Anadolu, a state-run news agency, said that the court decision was made due to his “health problems.”

Although Brunson denies the charges that have been filed against him, which carry a prison sentence of 35 years, he continues to be detained without trial by the Turkish authorities. On Tuesday, a court rejected Brunson’s appeal to be released altogether during his trial. In April, Brunson’s lawyer said that the allegations made against his client were “totally unfounded” and that the American pastor “was arrested due to his [Christian] faith.”

Brunson’s case has resonated with U.S. evangelicals, especially with conservative Christian and U.S. Vice President, Mike Pence, who recently attended a conference on religious freedom at the State Department, where anger over Brunson’s arrest was palpable.

During the conference organized by the Trump administration, Pence said, “To President Erdoğan and the Turkish government, I have a message, on behalf of the President of the United States of America. Release Pastor Andrew Brunson NOW or be prepared to face the consequences.”

Just half an hour later, U.S. President, Donald Trump, supported Pence’s threat of sanctions with a tweet that stated: “The United States will impose large sanctions on Turkey for their long time detainment [sic] of Pastor Andrew Brunson, a great Christian, family man and wonderful human being. He is suffering greatly. This innocent man of faith should be released immediately!”

Foreign Minister Çavuşoğlu responded to these threats by tweeting in English from his official Twitter account that, “[n]o one dictates Turkey [sic]” and that the country would “never tolerate threats from anybody.” Çavuşoğlu ended by emphatically saying that the “[r]ule of law is for everyone; no exception.”

The spokesperson for Turkey’s Ministry of Foreign Affairs, Hami Aksoy, also added that “[i]t is impossible to accept the U.S. Administration’s threatening message, which totally disregard [sic] our alliance and friendly relations between our countries.”

The relationship between the U.S. and Turkey is already on thin ice, as the former supports the Kurdish forces fighting in Syria, which the latter considers to be a terrorist group. Trump’s move to impose sanctions on two of Turkey’s top officials, the minister of justice, and minister of interior, for their role in the issue has only made the diplomatic situation worse.

After the announcement of the sanctions, the Turkish lira fell to a record low at 5.1140 against the dollar, resulting in a sell-off that hammered the Turkish stock market and its debt risk profile.

So, the question remains, why does Ankara insist on detaining Brunson if his detention could hurt Turkey’s economy and further strain relations with Washington D.C.?

Simply put, Erdoğan wants to use the evangelical pastor as a pawn to secure the extradition of U.S.-based cleric Fethullah Gülen. The cleric moved to the U.S. in 1999 after experiencing political and religious persecution in Turkey.

The inclusive brand of Sunni Islam that Gülen preached, which emphasized cooperation, tolerance and the compatibility of Islam with modernity, did not sit well with the then-Turkish Prime Minister Bülent Ecevit.

Since 2016, Erdoğan has called for the return of Gülen to Turkey, so he can stand trial for the failed coup that he allegedly fomented against the Turkish president. However, thus far, the U.S. has refused to approve Gülen’s extradition back to Turkey.

Even though Washington, D.C. is unlikely to agree to a one-for-one trade for Gülen, Ankara is also unlikely to give up Brunson, because Ankara knows how important this case has become in the American political arena.

Christian evangelicals form an important part of Trump’s political base. Consequently, securing Brunson’s release from Turkey would only serve to boost his popularity with his core supporters. However, Trump is not the only one in Washington, D.C. who wants to put pressure on Turkey.

Although Brunson’s story has received a lot of attention in the news recently, he is not the only person currently held by the Turkish authorities. The U.S. is also seeking the release of other detained American citizens and embassy staff.

Brunson’s detention has been cited as one of the main inspirations for a group of bipartisan U.S. senators, who drafted a bill that calls upon Ankara to stop detaining American citizens on false charges. The legislation introduced into the U.S. Senate on July 19 also aims to curb Turkey’s access to international loans.

After a rapid escalation in tensions between the U.S. and Turkey, the recent meeting of U.S. Secretary of State Pompeo and Turkish Foreign Minister Çavuşoğlu represents a move in the right direction if the two NATO allies want to mend their deteriorating relationship.

However, this act of goodwill alone will not be enough to restore the relationship between the two countries, if both sides continue to escalate the rhetoric and the measures they take to achieve their respective “hostage diplomacy” goals.