On July 4, 2003, U.S. paratroopers kicked down doors and raided a compound in the northern Iraqi city of Sulaymaniyah. It was two months after the United States declared “Mission Accomplished” and major military operations in Iraq over. The soldiers snatched up small arms, grenades, and explosives—and also 11 members of Turkey’s elite special forces. The U.S. troops reportedly cuffed the Turks and covered their heads with the kinds of dark hoods normally reserved for terrorist detainees in Afghanistan or Guantánamo Bay.

Before the Turkish commandos were released, it took days of behind-the-scenes diplomacy, including lengthy phone calls between then-Vice President Dick Cheney and then-Turkish Prime Minister Recep Tayyip Erdogan, to defuse the crisis.

The “hood incident,” as it’s still bitterly remembered in Turkey, barely registers as a footnote in U.S. histories of the Iraq War. For Turkey, it was emblematic of America’s willingness to act as it pleased with Turkey, a junior partner watching Washington trample its interests in the region, while the U.S. occupation of Iraq unraveled just across its border.

Fast forward 16 years and those same tensions and misunderstandings between two longtime NATO allies are as bitter as ever. Mistrust and mutual suspicion, like the hoods clapped on elite Turkish soldiers, define the relationship—and have done so almost from the moment the mutual enemy that originally brought Ankara and Washington together, the Soviet Union, disappeared nearly three decades ago. And many experts agree: The fault for the breakdown lies on both sides.

“In both countries, decisions regarding bilateral ties are marinated in anger before they are made,” said Soner Cagaptay, a Turkey expert with the Washington Institute for Near East Policy.

Nothing illustrates this better than the bitter, nearly decade-long fight over Turkish defense systems, which began when the United States refused to share sensitive missile technology with Ankara related to the U.S.-made Patriot air defense battery. Turkey eventually turned to Moscow for help, and a whole new spiral of mistrust began.

The delivery this month to Turkey of the Russian-made S-400 missile defense system—despite repeated and vociferous threats and warnings from Washington—has now prompted the United States to question its fundamental ties with Turkey in a way that it hasn’t in almost seven decades of partnership. As part of NATO, Turkey is officially an ally. But is it a friend? And what are the risks of parting ways with a nation that serves as the southeastern bulwark of the Western alliance?

“Turkey is neither an ally nor an enemy. It is an antagonist of the United States.”

“There has been a complete breakdown in trust between the United States and Turkey,” said Amanda Sloat, a scholar at the Brookings Institution and a former U.S. diplomat. “The dispute over Turkey’s purchase of Russian military equipment is the latest in a long list of bilateral grievances. In short, Ankara wonders if Washington cares about its security needs, and Washington wonders if Ankara is a reliable ally.”

Ankara’s move cost it access to the U.S. F-35 fighter jet and sparked congressional efforts to slap sanctions on Turkey’s already faltering economy. When a NATO ally buys advanced Russian weapons, and spurns the chance to bolster its own forces with cutting-edge U.S. defense technology, risking economic catastrophe in the process, it’s a breach of historical proportions. Since the earliest days of the Cold War, Turkey had been more or less firmly anchored in the U.S.-led Western order. Now, it’s throwing off old ties, and analysts fear it is looking more to Moscow than to Washington; a day after the United States formally kicked Turkey out of the F-35 program, Moscow offered to sell Turkey its own advanced fighter, the Su-35.

“There’s a lot of mythology about the relationship since 1952,” when Turkey joined NATO, said Steven A. Cook, a Middle East scholar at the Council on Foreign Relations. “But I am not aware of a situation like we have today, where the Turks seem to be moving closer to Moscow.”

Turkey is not working toward the same goals as the United States in Syria, it still has frosty relations with Israel, and it’s ratcheting up tensions—despite warnings from the United States and the European Union—over energy exploration around Cyprus and is giving Russia entree to ship more natural gas to Europe against Washington’s wishes. After decades of axiomatically considering Turkey an ally, policymakers in Washington are suddenly adrift. Some analysts are torn on how to define the relationship.

“Turkey is neither an ally nor an enemy,” Cook said. “It is an antagonist of the United States.”

It’s unclear how far Washington will go to retaliate for Turkey’s purchase of the Russian-made S-400. The U.S. Defense Department has been clear that the F-35 can’t operate alongside sophisticated Russian weapons that could give Moscow insights into the stealth fighter, and Turkey has already been cut out of the jet program. U.S. legislation mandates economic sanctions on countries that buy certain Russian-made weapons, but U.S. President Donald Trump could still seek to offer Turkey some wiggle room, either by delaying the imposition of sanctions or watering them down. That, in turn, would likely prompt Congress, which has lost its patience with Turkey, to redouble punishing sanctions legislation.

Since the very dawn of the Cold War, Turkey has been an anchor in the U.S. security system. The Truman Doctrine began seeking to shield Greece and Turkey from Soviet threats; Turkey joined NATO soon after to gain protection from an expansionist Soviet Union. For decades after, despite plenty of tensions, disagreements, and differing regional priorities, many in Washington considered Turkey a vital and necessary strategic partner, the keystone to NATO’s southern flank, and a Western-friendly bridgehead in the Muslim world.

But despite Washington’s inclination to do whatever it took to keep Turkey onside, Ankara’s purchase of the S-400 was a “bridge that couldn’t be crossed,” said Howard Eissenstat, a specialist on Turkey at St. Lawrence University.

Now, after years of overlooking Turkey’s erosion of democracy and disruptive regional diplomacy in the hope of keeping the security relationship on a sound footing, lawmakers and many others in Washington are in a vengeful mood. And experts fear their anger will only be self-defeating—potentially opening up a permanent rift with Turkey that could weaken the U.S. and NATO’s position in a critical part of the world.

“I worry that U.S. policy will shift from trying to keep Turkey on board to trying to crush them to show the costs of crossing the United States, which would be self-destructive,” Eissenstat said.

How did the two countries get to this point? Or, to paraphrase the foreign-policy debates that dominated 1950s Washington after China went communist: Who lost Turkey?

To understand how the two NATO allies have reached a point of outright antagonism requires a long journey back in time—to simmering tensions during the Cold War; U.S. policy missteps toward Iraq in the 1990s and 2000s; the rise of a nationalist, Islamist Turkish leader determined to make the country an independent regional power; and, most crucially, a fatal dialogue of the deaf during the ongoing Syrian civil war, when U.S. support for Kurdish fighters fanned Ankara’s deepest insecurities and Turkey’s unwillingness to fight the Islamic State dismayed successive U.S. administrations.

Ultimately, the U.S.-Turkish strategic alliance would be hard-pressed to survive the post-Cold War transition to a multipolar world.

“Looking back, you could say it was a chronicle of a death foretold,” Cook said. The disappearance of the Soviet Union was followed shortly after by the rise of a more nationalist Turkey after the turn of the century “that didn’t want to just be an appendage of the West, doing the bidding of the United States.”

“Looking back, you could say it was a chronicle of a death foretold.”

Turkey is a crossroads, straddling Europe and Asia, bordering Iran and the former Soviet republic of Georgia, and flanked on its southern border by Syria. That, as much as politics, may explain Ankara’s eagerness to embrace multipolarity before other NATO allies did.

“After the Cold War, any Turkish government would have tried to carve out a more independent foreign policy and a more prominent regional role,” said Nicholas Danforth, a Turkey expert at the German Marshall Fund of the United States. “The difference is, you could have that in a way that was compatible with Western interests or one at odds with Western interests.” And that, it turns out, was true in both directions: U.S. policy could also end up at odds with Turkey’s deepest needs.

The relationship early in the Cold War makes it easy to understand how generations of U.S. policymakers came to view Turkey as an indispensable ally. When Turkey joined NATO in 1952, it brought the alliance its largest land army and priceless geography. In 1954, the United States gained access to the superbly located Incirlik Air Base, which remains a key launching pad for U.S. operations in the Middle East and also houses U.S. nuclear weapons. A year later, Turkey joined the Baghdad Pact, a Middle East anti-communist grouping.

But even in the Cold War years, there were sharp breaches between the two countries. Already in the 1960s, Presidents John F. Kennedy and Lyndon Johnson had diplomatic dust-ups with Turkey. In the 1970s, after Turkey invaded the northern half of Cyprus and set up a breakaway Turkish republic, Washington responded with years of arms embargoes.

Ross Wilson, who served as the U.S. ambassador to Turkey from 2005 to 2008, said in some ways the arms embargoes over Cyprus foreshadowed Turkey’s mistrust of the United States as an arms supplier. “It severely curtailed Turkey’s ability to buy [equipment] from us for that period and raised questions about America’s reliability” on defense purchases decades later, he said.

In retrospect, the first big challenge to the post-Cold War order—the 1990-1991 Gulf War—pried open one of the crucial fissures in the relationship that would later became a chasm.

While Turkish policymakers and the military broadly supported the U.S. attack on Saddam Hussein’s Iraq, they were concerned about the emergence after the war of a quasi-independent Kurdish state in northern Iraq. For Turkey, Kurdish nationalism is a potentially existential threat—the country has spent decades battling a Marxist-tinged Kurdish militant group, known as the Kurdistan Workers’ Party (PKK) and has deep-seated fears that any Kurdish homeland would pose a severe security threat.

President George H.W. Bush’s protection of northern Iraqi Kurds from Saddam’s forces after the war fueled Turkish suspicions that Washington was—wittingly or not—bolstering Kurdish militants.

“Turkey had paranoid fears of U.S. support for independent Kurds after the first Gulf War,” Danforth said. It was a paranoia that, to Turkish eyes, would in decades to come be amply borne out as Washington boosted its support for Kurdish forces, even as it stopped short of advocating full Kurdish independence.

One night near midnight in early 2003, on the eve of the U.S. invasion of Iraq, an officer from the U.S. Joint Chiefs of Staff rushed into the office of Jim Townsend, a Pentagon official working overtime to get U.S. allies on board with the invasion plans.

“He goes, ‘OK, we need you to show us the line through northern Iraq where Turkish troops can come down to,’” Townsend recalled. In exchange for allowing U.S. troops to hit Iraq through Turkey, Ankara, wary of how Kurdish influence grew in Iraq amid the Gulf War, wanted to send its own military into northern Iraq to have a bigger say in the country post-invasion.

“‘I need it, like, right now. Point out on this map where the line is,’” the frantic officer begged, apparently in the midst of rushed negotiations with Turkish counterparts. Townsend struggled to respond. “I said, ‘I’m sorry, I just don’t know where the line is or even if there is a line. I don’t want to just make something up on the spot.’”

Ultimately, the Pentagon’s efforts to get Turkey on board with the U.S. invasion failed, and the Iraq War would see the first major break between the two allies since the bad blood over Cyprus decades before. In the spring of 2003, the Turkish parliament, with Erdogan as the head of the newly victorious Justice and Development Party (AKP), failed to give permission for a U.S. Army division to invade Iraq via Turkey—upsetting U.S. military planning and sowing years of ill will in the Pentagon. Erdogan feared that an invasion of Iraq would be destabilizing and would ultimately reignite Kurdish violence. The Turks were also still smarting from the fact that the United States never delivered on promised reimbursement of Turkish economic losses from actions they took during the Gulf War in 1990-1991.

“If you want to start dating when things really started going downhill, a lot of it started with [the Turkish government] coming back to us in the hours before we invaded Iraq saying, ‘We’re not going to play ball with you,’” Townsend said. “Within the Pentagon bureaucracy, among our military, the Turks were seen as screwing us.”

Turkey came “back to us in the hours before we invaded Iraq saying, ‘We’re not going to play ball with you.’ … Among our military, the Turks were seen as screwing us.”

“The problem was how much U.S. policymakers had misunderstood about Turkey. It used to be, you could call up the generals, and they would fall into line. But even the generals were opposed” to the Iraq War, Cook said.

Months after the invasion, when the soldiers of the 173rd Airborne Brigade hooded Turkish troops as they tried to pacify a bubbling insurgency in northern Iraq, those misgivings seemed ever more justified in the Turkish government’s eyes.

And a year after the invasion, when the PKK called off its cease-fire and again began killing Turkish troops after a five-year respite, the mistake, in Turkish eyes, was clear.

“That was hugely underappreciated in Washington: The Turks warned the United States that the invasion of Iraq would undermine their stability, and it did, and we said we had other priorities,” Cook said.

Those geopolitical tensions coincided with a political shift inside Turkey of historic proportions. A year before the Iraq War, the AKP won the Turkish elections—and has held power ever since. Led by Erdogan, an Islamist with visions of restoring the prestige and greatness of the lost Ottoman Empire, Turkey threw aside the country’s secular roots of governance and traditional reliance on the West and set out to chart a truly independent foreign policy. Turkey’s refusal to grant access to the U.S. Army during the invasion of Iraq was just one manifestation of a more democratic but also more assertive and independent Turkey.

At this time, as Erdogan solidified his grip on power, there was another potential missed opportunity that has left some Western officials pondering over whether Turkey’s democratic institutions, at one point thriving but now a shambles, could have been saved: the prospect of joining the European Union.

In the mid-2000s, even as U.S.-Turkish relations were deteriorating, Turkey was in accession talks to join the European Union, buoyed by a pro-Western population and the promise of integrating with the world’s largest economic bloc. The price was undergoing wide-ranging government reforms designed to strengthen Turkey’s democracy.

But those efforts stalled in 2008 and 2009, amid opposition from Germany and France, as well as Cyprus—the island still divided after Turkey’s 1974 invasion—using its perch as a relatively new EU member to block a batch of accession negotiations.

“The EU, had it not failed to allow the accession process to basically stall … I think could have remained a much stronger voice in Turkish society for democratic values,” said Wilson, the former U.S. ambassador.

The EU’s attitude made it “easy for the Turks to get the sense that even if they reformed everything, they were still going to be, as the saying went at the time, ‘too big, too poor, and too Muslim’ to join,” Danforth said.

EU accession talks with Turkey are still technically ongoing, but most analysts say the process is effectively dead in the water.

Even as talks with the EU stalled in the late 2000s, Erdogan was busy cementing his political power at the top. For a brief time in his political ascent, he enlisted the help of Fethullah Gulen to shore up his political position. Gulen, a wealthy U.S.-based Turkish cleric, established a broad base of support in parts of Turkish society through an expansive business empire that had its reach in the education system, media, and financial institutions. His support in part helped Erdogan clinch an important 2011 victory for the AKP.

But that marriage of convenience quickly dissolved after Erdogan’s government became embroiled in corruption scandals that culminated in a massive wave of protests in 2013. Erdogan blamed Gulen for inciting the protests, sparking a rift between the two that never healed and eventually became the centerpiece of Erdogan’s response to a dramatic coup attempt in 2016.

Erdogan’s fears only intensified in the years after the Arab Spring—and especially after the Egyptian army’s overthrow in 2013 of the country’s democratically elected Islamist president, Mohamed Morsi, a coup that the United States accepted with little protest. Coinciding with Turkey’s 2013 protests—named after Gezi Park in Istanbul, where they started—Erdogan began to see the dark hand of Western conspiracy, enlaced with Gulen’s influence, everywhere.

Erdogan blamed Fethullah Gulen for inciting the protests, sparking a rift between the two that never healed.

“The sense of Western perfidy that Erdogan saw with Egypt, he was very explicit about seeing Morsi’s overthrow as one iteration of a larger story in which Western forces are attempting to control the world,” Eissenstat said.

When Turkey looked around the region, what it saw only fueled its fears. Western countries, led by the United States, pushed for regime change in Libya, which led to the death of Muammar al-Qaddafi, and were calling for the ouster of Syria’s brutal strongman, Bashar al-Assad. Turkey’s pro-American Middle Eastern rivals, led by Saudi Arabia, would eventually blockade Qatar, one of Turkey’s only friends in the region. A brief thaw in Turkish relations with Israel was dramatically cut short in 2010 after Israeli forces stormed a Turkish ship sent to aid Palestinians in the Gaza Strip.

“From Turkey’s point of view, they all fit together as evidence of Western hostility, and it all had a cumulative effect of making foreign policy seem much more existential than it otherwise might have been,” Danforth said.

For Turkey, a seemingly existential foreign-policy crisis was just beginning—exacerbated, in Turkish eyes, by the U.S. approach to fighting jihadis in the middle of the Syrian civil war, which began in the spring of 2011 and continues to this day.

While the United States under President Barack Obama said it wanted to see Assad leave power, the main focus of U.S. military efforts in Syria was aimed at Islamist terrorists. And that focus was especially on the Islamic State, which used the war in Syria and a breakdown in security in neighboring Iraq to create the first caliphate since just after the end of the Ottoman Empire nearly a century earlier.

For Washington, the fight against the Islamic State took absolute priority; for Turkey, the biggest threat coming out of Syria was not jihadis but armed Kurds who were steadily carving out territory in northern Syria, on the border with Turkey.

Casting about for a reliable fighting force on the ground to complement U.S. air power, Washington by 2015 almost by default settled on Kurdish fighters grouped in People’s Protection Units (YPG). The YPG, formed about a decade earlier, was seen by both Turkish and U.S. officials as essentially the armed wing of the very Kurdish groups, especially the PKK, that for decades bedeviled Ankara. The United States itself had designated the PKK a terrorist group in 1997 but made room to work with armed Kurdish fighters in Syria because U.S. officials felt there were no viable alternatives.

“Essentially, the United States misread Turkey’s priorities in the war,” Eissenstat said, thinking that the fight against the Islamic State, also referred to as ISIS, overshadowed Turkey’s historical obsession with preventing a transnational Kurdish state. “But Turkey didn’t see that the United States was going to do something about ISIS and needed a land fighter—the options were either the Turkish army or the YPG.”

But Ankara never put the Turkish army at the service of Obama’s fight against the Islamic State and even erected roadblocks in the U.S. use of Turkish facilities—including Incirlik Air Base—to carry out operations. That led to a fatal misunderstanding that ultimately poisoned the relationship and eventually to Erdogan’s willingness to throw out ties with Washington altogether.

“The key arena was Syria. U.S. frustration with Turkey’s inaction, coupled with Turkey’s anger at U.S. support for the YPG, brought into question some of the foundations of the relationship,” said Robert Malley, Obama’s Middle East advisor from 2014 to 2017.

“Washington felt Ankara was always promising far more than it would deliver in the fight against ISIS, and Ankara considered U.S. backing for the Kurdish group an act of betrayal,” said Malley, now the president and CEO of the International Crisis Group.

The Obama administration, spearheaded by Vice President Joe Biden, sought repeatedly to reassure Turkey about the deepening U.S. cooperation with Kurdish forces—but collided with Turkey’s deep-rooted fears.

“Every time the Obama administration took a step in the direction of the Kurds, it was preceded by an effort to placate the Turks,” Malley said. Obama had to weigh his desire to tackle the Islamic State against the desire not to alienate Turkey or Erdogan.

“But when, in the administration’s judgment—rightly or wrongly—it appeared that Turkey was not prepared to do enough and that the only party on the ground willing to decisively take the fight to ISIS was the YPG, Obama felt he had no choice,” Malley said.

“The only party on the ground willing to decisively take the fight to ISIS was the YPG. Obama felt he had no choice.”

The U.S. engagement with Kurdish fighters came just as Turkey was raising objections to the U.S. use of Incirlik, the best-placed airfield for carrying out strikes against the Islamic State. For a full year, the two NATO allies haggled over America’s ability to fully utilize an air base that—in U.S. eyes—had for decades served as a security umbrella for Turkey.

“From the U.S. point of view, it had always been our base, and the Turks think it is theirs. That’s a perfect example of the kind of tensions that go back to the 1950s,” Danforth said.

The drawn-out negotiations with a NATO ally over using Incirlik to take the fight to the Islamic State “drove people bonkers,” Cook said. “It made an impression on people in the Pentagon who already had a jaundiced view of Turkey because of the Iraq War.”

If mistrust and misunderstanding between the United States and Turkey were already at a fever pitch by 2016, they were about to get a whole lot worse. On July 15, 2016, elements of the Turkish military staged an abortive coup against Erdogan. Turkish F-16 jets taking off from Incirlik trailed the presidential plane after Erdogan narrowly escaped capture at his coastal villa. Another one bombed the parliament.

For agonizing hours, it was unclear whether the generals had ousted Erdogan or not—and when an opportunity arose to publicly back Erdogan as the coup plot unfolded, Washington and other European powers balked.

As they hesitated, Russian President Vladimir Putin jumped into the vacuum, becoming one of the first foreign leaders to call Erdogan and denounce the coup attempt. It proved to be a diplomatic fait accompli for Putin, pushing Turkey further into Russia’s orbit and shoring up Moscow’s growing influence in the Middle East after Russia’s military intervention in Syria to back Assad.

“Putin saw an opening that this could be a beginning of a permanent rift between Ankara and Washington because meanwhile the U.S. government [hesitated] to respond to the coup,” said Cagaptay, the Washington Institute expert.

“Putin saw an opening that this could be a beginning of a permanent rift between Ankara and Washington.”

After Erdogan emerged from the botched coup attempt unscathed, he set out on a nationwide campaign of reprisals, firing more than 100,000 public servants, arresting more than 40,000 people, and expanding his presidential powers to root out dissent. Both Washington and European allies grew increasingly alarmed over Erdogan’s dismantling of democratic institutions and crackdown on free press and civil society. The prospect of joining the EU—even as Turkey bore the brunt of the European refugee crisis amid the Syria conflict—became all but a pipe dream.

Many in Turkey believe the United States either played a role in the coup or knew about it in advance—charges that U.S. officials have consistently and vehemently denied—further estranging Turkey’s government and public from the United States. One big reason is that Gulen, the Turkish cleric and former political ally of Erdogan’s whom he blamed for orchestrating the coup plot, resides in the United States. The U.S. Justice Department has refused to bow to Turkish demands to send him to Turkey to face charges, saying Turkey has not produced enough evidence to justify any extradition request.

“Erdogan thinks if the U.S. wants to extradite Gulen, it can do so in a day because that’s how things work on the Turkish end,” said Aykan Erdemir, a Turkish former member of parliament now at the Washington-based Foundation for Defense of Democracies. “There’s the inability to fathom the separation of powers in the U.S. and that the judicial branch is independent. … This is difficult to imagine for Erdogan and for a vast majority of his loyalists,” he said. “This all just poisons the relationship further.”

With the surprise election victory of Donald Trump in 2016, prospects of better U.S.-Turkish relations seemed in the cards. Trump and Erdogan shared a fondness for authoritarianism, a disdain for a free press, and a willingness to reach out to Russia. More to the point, from Ankara’s perspective: Trump’s incoming national security advisor, Michael Flynn, was on the payroll, actively lobbying for Turkish interests during the presidential transition and even after the inauguration. (Flynn even reportedly sought to arrange the extrajudicial extradition of Gulen from the United States—something Turkey had sought in vain for years.)

Yet despite the personal affinity between the two presidents, which appears to continue despite the rift between the two countries, Trump’s arrival didn’t alter the fundamental trajectory of the relationship. Months after the abortive coup, Turkey had detained a U.S. evangelical pastor working in Turkey, Andrew Brunson, on charges of terrorism. In 2017, Erdogan sought to swap Brunson for Gulen, whom the since-ousted Flynn had failed to deliver, but the United States refused. By 2018, the Trump administration levied sanctions on senior Turkish officials to force Brunson’s release.

Coming amid the continued crackdown on democracy in Turkey in the wake of the coup attempt, the misunderstandings between Erdogan and Trump mirrored the broader breakdown in a relationship that had already gone off the rails in Syria.

“Domestic developments in both countries in the last two years have not made dialogue any easier,” Danforth said. “There’s a level of confusion that Trump brought about how Washington works, that made it easier for Turkey to imagine that it works more like Turkey does.”

Those misunderstandings have been on full display during the crisis over the S-400. Turkey, which had for years sought to acquire U.S. air defense systems and all the associated technology, was repeatedly rebuffed by Washington. In 2015, it sought to purchase Chinese missiles, which the United States and NATO scuppered. Eventually, it turned to Russia for arms, hoping to force the United States to reconsider. But for U.S. defense officials, that technology transfer was always a nonstarter—and the Turkish purchase of the S-400 is utterly at odds with Turkey’s acquisition of the latest U.S. aircraft.

“What’s different here, more than anything else, is that a lot of the other past disagreements within the NATO alliance have been political. But this one is a military one,” said Townsend, the former Pentagon official. “For the first time, a nation has done something more than just political. It’s actually done something … that imperiled the alliance’s ability to use its military.”

Congress, the State Department, and the Pentagon have all been clear about the consequences of a missile purchase from Russia. So why did Turkey press ahead, regardless?

Some analysts lay the blame at Trump’s feet. The U.S. president has muddied the waters with his warm personal dealings with Erdogan, at times appearing to reassure the Turkish president that the two countries can work something out.

Even this week, the Trump administration went silent for four days before announcing on Wednesday that it would cut out Turkey from the F-35 program as the first response. Trump on Thursday said he hadn’t yet decided on whether to impose sanctions on Turkey, though members of Congress on both sides of the aisle have said Trump can’t get around sanctioning Turkey. Trump also still harbors misgivings about the Obama administration’s role in Ankara’s decision, saying “the previous administration made some very big mistakes” on Turkey.

Erdogan’s push to buy the S-400 also has its roots in the coup attempt, which deeply scarred him and traumatized the Turkish public. Beyond geopolitics or animosity toward Washington, Erdogan simply wants to survive should another coup attempt arise. After facing down U.S.-made F-16s in the 2016 coup attempt, his thinking is driven by what would be the best missile system to stop any Western fighters, some analysts say. Naturally, the answer lies with a Russian-made system.

“That point is not well understood [in Washington], but it’s key to this deal,” said Asli Aydintasbas of the European Council on Foreign Relations.

As Turkey takes delivery of advanced Russian weapons, it is also moving closer to Moscow in the energy sector, including TurkStream, a major gas pipeline from Russia’s Black Sea coast to Turkey meant to supply both the local market (Russia’s second-biggest European customer) and, in the future, southern Europe.

Turkey’s decision to spurn Washington on the S-400 deal, and growing U.S. concerns about how Erdogan is drawing close to Putin, has alarmed U.S. policymakers and lawmakers. Even if Trump manages to soften or delay those, Congress is in no mood to be conciliatory. “If there’s one thing that unifies Congress right now, it’s Turkey,” Cook said.

And Congress could, as it has in recent years regarding Russia, draft tougher, more specific sanctions legislation to close any loopholes the president might exploit.

“Even if Trump lets Turkey off the hook, the problem doesn’t go away. Turkey will be more emboldened, and Congress will get even madder, so it just sets the stage for another showdown,” Danforth said.

But beyond the defense and economic fallout, Turkey’s embrace of Russia raises questions that are now more acute than at any time since the middle of the 20th century: Is Turkey still really part of NATO? Is the lurch toward Russia a marriage of convenience—or a permanent shift?

Aydintasbas said Erdogan’s turn east could be fleeting, as he comes to realize Russia isn’t an ideal ally in Syria or elsewhere. “If the ebb and flow of Turkish-Russian relations in the past 300 years is any indication, it is likely that this round of rapprochement will also end in disappointment,” she said.

Even if NATO could kick Turkey out of the alliance, there seems to be no appetite in Washington or any NATO capitals to do so, given Turkey’s historic and geopolitical importance as a member. “Turkey is an important NATO member, and no ally has raised that issue,” NATO Secretary-General Jens Stoltenberg said at a security conference on Wednesday when pressed on the issue. “Turkey, as a NATO member, is much more than [just the] S-400.”