Understanding Turkey’s rollercoaster relations with the U.S. requires a grasp of advanced military hardware. Turkey says its army, NATO’s second-largest, will take delivery of Russia’s S-400 missile-defense system in early July. President Donald Trump’s administration contends that could help Moscow gather critical intelligence and it’s threatened sanctions that could cripple Turkey’s economy. Turkish leader Recep Tayyip Erdogan is betting his personal rapport with Trump will fend off harsh penalties. But with Congress vigorously against the missile deal, there’s a high risk of punishments that could plunge Turkey into renewed economic turmoil.

1. Why is the U.S. so opposed to the deal?

The S-400, also known within NATO as the SA-21 Growler, has advanced radars and isn’t compatible with alliance technology. Its deployment in Turkey would mark a further advance in Russian President Vladimir Putin’s efforts to engineer a bigger role in the Middle East. Chief among U.S. concerns is that the Russian system could be used to collect intelligence on the stealth capabilities of the U.S. F-35 fighter jet that Turkey is buying and helping to build. There’s history here. Turkey is home to the Incirlik Air Base, used for U.S. operations against Islamic State and, decades before that, the main operating location for the American U-2 spy plane -- until American pilot Francis Gary Powers was famously shot down over the Soviet Union in 1960.

2. What explains Turkey’s determination to press ahead?

Erdogan says Turkey’s western allies failed to provide his country the necessary defense against missile threats from neighboring Iran, Iraq and Syria. And while the U.S., after years of objections, agreed to sell Patriot air defense missiles to Turkey in an apparent effort to get Erdogan to scrap the S-400 deal, it’s not clear lawmakers would let the sale go through because of anti-Turkey sentiment in Congress. Turkey’s determination to defy the sanctions threats reflects a desire for an increasingly independent role in regional policies and for economic ties with Russia. Officials say Turkey also has lost trust in the U.S. because of disagreements on multiple fronts.

3. How else has Turkey asserted military independence?

Turkey’s defense industry developed its own unmanned drones, ending a dependence on Israeli ones, and it aspires to build sophisticated ballistic missiles and fighter jets. Turkish military spending surged 65% between 2009 and 2018, according to the Stockholm International Peace Research Institute, which researches global arms expenditure. Last year, its spending rose at the fastest pace among the world’s top 15 arms purchasers to $19 billion.

4. How far might the U.S. go?

The U.S. warned that Turkey faces expulsion from Lockheed Martin Corp.’s F-35 program. Turkish companies were set to produce about $12 billion in parts for the jet, and the Turkish air force planned to buy about 100 planes. Deliveries of F-35 equipment to Turkey have been suspended. U.S. Secretary of State Michael Pompeo signaled that the estimated $2 billion S-400 purchase could also trigger sanctions against Turkey under the U.S. Magnitsky Act and other legislation that allows penalties on entities doing business with parts of the Russian state. The last time the U.S. sanctioned Turkey, over the arrest of an American preacher, the ensuing collapse in the value of the Turkish lira hastened the country’s first recession in a decade.

5. What else have the U.S. and Turkey been sparring over?

Plenty. Their six-decade alliance has been strained by U.S. support for a Syrian Kurdish militia that Turkey considers a foe, and Washington’s refusal to extradite Fethullah Gulen, the Turkish cleric living in exile in Pennsylvania whom Erdogan accuses of orchestrating a failed 2016 coup. Things were inflamed further by Turkey’s detention of the American pastor, Andrew Brunson, and employees of U.S. diplomatic missions in Turkey on suspected involvement in the attempted putsch or terrorism. Ankara is also miffed that Washington is backing Turkey’s rivals in a natural gas dispute with Cyprus and in other regional conflicts.

6. Is there a path to a compromise?

Having served as a bulwark against Russia during the Cold War, Turkey believes it has valuable bargaining chips. It still hosts American nuclear warheads at Incirlik and military installations used by the U.S. to spy on Russia. It’s also the only barrier keeping more than 4 million refugees, most of them Syrians, from flooding into Europe. Erdogan plans to discuss the S-400 purchase with Trump at the Group of 20 summit this month. And there’s also the personal chemistry with Trump.

The Reference Shelf

• Related QuickTakes on U.S.-Turkey tensions, the Magnitsky Act, Turkey’s distrust of U.S., power struggles, U.S.-Turkey feuds, Turkey’s economic travails, U.S.-backed Kurdish forces and the Syrian war.

• A Congressional Research Report on Turkey contains a section on Turkish foreign policy.

• A Bloomberg Opinion editorial on the conflict over the S-400.

To contact the reporter on this story: Selcan Hacaoglu in Ankara at shacaoglu@bloomberg.net

To contact the editors responsible for this story: Leah Harrison Singer at lharrison@bloomberg.net, ;Onur Ant at oant@bloomberg.net, ;Benjamin Harvey at bharvey11@bloomberg.net, Mark Williams

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