TURKEY’S ECONOMY is in crisis, teetering on the brink of an implosion that could undo two decades of progress. President Recep Tayyip Erdogan is blaming economic warfare by President Trump, who last week announced a doubling of tariffs on imports of Turkish aluminum and steel . The U.S. action was ill-advised, in part because it may confuse Turks about who is really responsible for the collapse of the national currency: none other than Mr. Erdogan himself.

Since winning election to a newly empowered presidency in June, Mr. Erdogan has accelerated a shift toward one-man rule that has unnerved the foreign investors and lenders upon whom Turkey heavily depends. He installed his son-in-law as finance minister and has used his sway over the central bank to prevent a desperately needed rise in interest rates. The predictable result has been a precipitous drop in the value of the Turkish lira against the dollar, which in turn threatens to bankrupt the many companies and banks that have taken foreign loans.

The economic mismanagement is a piece of Mr. Erdogan’s increasingly megalomaniacal rule, which has included massive domestic repression and deluded attempts to bully other states, including Israel, Germany and Russia. The Turkish ruler eventually backed down from those battles, only to take on his country’s closest military ally: the United States.

In an apparent attempt to force a U.S. handover of an ally-turned-rival who lives in Pennsylvania, Mr. Erdogan imprisoned a number of American citizens on trumped-up charges, including a pastor, Andrew Brunson, whom Mr. Erdogan has openly described as a bargaining chip. Mr. Trump thought he made a deal with the Turkish strongman in a July meeting to free Mr. Brunson; when the Turks failed to deliver, an angry White House imposed sanctions on two Turkish government ministers before announcing the new tariffs.

One problem with the administration’s response is that it is too narrowly focused on Mr. Brunson, who has become a cause celebre for Christian evangelicals. Mr. Trump ought to be demanding that all 20 U.S. citizens being held be released, along with several Turkish employees of U.S. consulates. In addition, the use of tariffs as a political weapon is a dangerous breach of international norms. The administration would have done better to expand on the sanctions against individuals involved in the improper detentions and other human rights abuses, and to hold up, as Congress has mandated, delivery to Turkey of F-35 fighter jets.

The decision to get tough with Mr. Erdogan is nevertheless the right one. Analysts who worry about a fracturing of relations with a key NATO ally ought to recognize that Turkey has not been behaving as an ally; allies do not take U.S. citizens hostage. Fears that the currency crisis will spread to other developing nations so far look exaggerated. Mr. Erdogan’s own threats to turn to Russia look empty; Moscow cannot supply the billions of dollars needed to pull Turkey’s economy out of the hole he has dug.

Mr. Trump evidently believes that he has decisive leverage over Mr. Erdogan, and he is probably right. He should use it not just to free one Christian pastor but also to show an unhinged ruler the costs of playing dictator, either to his own people or to the rest of the world.

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