Andrew Brunson, an American pastor, stands in Izmir, Turkey, in this undated photo. He is imprisoned in Turkey, and his case is set to begin Monday. (DHA-Depo Photos via AP)

Eric Edelman, a former U.S. ambassador to Turkey (2003-2005), is a senior adviser at the Foundation for Defense of Democracies. Aykan Erdemir, a former member of the Turkish parliament (2011-2015), is a senior fellow at the Foundation for Defense of Democracies.

On April 16, an American pastor unjustly detained in a Turkish prison for 18 months will finally get to defend himself in court. Andrew Brunson, a Presbyterian minister from North Carolina, faces up to seven years of pretrial detention under Turkey’s draconian state of emergency. Brunson is not a prisoner but a hostage, whom Turkish President Recep Tayyip Erdogan is cynically using to extort concessions from the United States, a fellow member of NATO. It is high time for President Trump to press for Brunson’s immediate and unconditional release.

For over 20 years before his sudden arrest, Brunson had preached peacefully in Turkey’s third-largest city, Izmir. Initially, Turkish authorities charged Brunson with membership in an armed terrorist organization. Later they added charges of espionage and attempting to overthrow the government, although there is no evidence to support any of these accusations. Brunson’s attorneys finally received the indictment last month, but only after it had been leaked to the media. The 62-page indictment is a muddled collection of conspiracy theories based largely on ludicrous accusations from three “secret witnesses.” If convicted, Brunson faces a life sentence.

Brunson is a respected member of his community and didn’t quit his post even after surviving a far-right militant’s armed attack in 2011. When Turkey’s religious minorities, particularly Christians and Jews, became scapegoats following the abortive coup in July 2016, Brunson, like many other church leaders, came under increasing pressure.

Turkey’s pro-government media has been shameless in its smear campaign against Brunson. The media claimed that the pastor would have become the next director of the CIA had he been successful in helping to coordinate the attempted coup against Erdogan. When there was a bomb attack against wardens of the maximum-security prison where Brunson was being held, a story accusing the CIA of masterminding the attack ran under the headline “The Pastor’s Bomb.”

The targeting of Brunson, however, is not simply the result of the post-coup-attempt rise in chauvinism in Turkey. Ankara, borrowing Iran’s tactic of holding Western nationals captive, has launched a campaign of hostage diplomacy. Since the abortive coup, Turkish authorities have arrested on dubious charges not only U.S. citizens and consular staff but also British, Czech, Dutch, French, German, Greek and Swedish nationals, including journalists, academics, human rights activists and a Christian pilgrim on his way to Jerusalem.

Last September, shortly after issuing an emergency decree giving himself the authority to trade foreign nationals held in Turkish prisons for individuals incarcerated abroad, Erdogan publicly offered to release the pastor, proposing a prisoner exchange with the United States that would involve the extradition of Fethullah Gulen, a Turkish cleric living in Pennsylvania. Gulen leads a shadowy network whose members appear to have played a central role in the 2016 coup attempt.

When Erdogan made this swap offer last September, he was actually aiming for an exchange that involved Reza Zarrab, the Turkish-Iranian gold trader who was scheduled to stand trial in New York in November for evading sanctions against Iran. The Turkish president wanted to prevent Zarrab from revealing information to U.S. authorities that might implicate Erdogan in grand corruption. Zarrab’s attorneys confirmed swap rumors by stating to the judge that they had been looking for a “diplomatic solution,” a euphemism for a shameless trade that would release a sanctions-busting suspect in exchange for an innocent hostage.

Erdogan’s reckless hostage diplomacy is hurting not only Turkey’s image but also its relations with the United States and other NATO allies. The U.S. Congress sent a letter to Erdogan seeking the unconditional release of Brunson. In addition, the Senate Appropriations Committee passed an amendment providing additional authority to the State Department to impose sanctions on Turkish officials involved in his case. President Trump has raised the issue multiple times in his meetings with Erdogan.

So far, Erdogan’s hostage diplomacy hasn’t borne fruit, since neither the United States nor any European Union country has taken up his proposed swaps. On the other hand, members of the transatlantic alliance have not made Erdogan pay a price for his abuse of their citizens.

If Erdogan had a serious interest in bringing home Turkish suspects who reside in Western countries, the more effective approach would be to enable legitimate extraditions by showing that repatriated Turks could expect fair trials upon their return. But this would mean abolishing Turkey’s state of emergency and reinstating essential aspects of the rule of law, such as due process and attorney-client privilege. Instead, Erdogan threatens to reinstate capital punishment, while the state media shows off tortured detainees.

As the West has learned from dealing with Iran, negotiating for the release of hostages only encourages more hostage-taking. The United States and its allies should refuse to dignify Erdogan’s demands. And they should vigorously pursue legal action against corrupt lawbreakers whom the Turkish president desperately wants to protect. The only thing that will compel Erdogan to stop targeting Western nationals is a relentless determination to resist his swap deals and expose his authoritarian tactics.