Turkish-American relations are often fraught with drama followed by reconciliation. In the end, the two countries usually manage to save their partnership by focusing on shared strategic interests. But in recent years, they have had increasingly different threat perceptions and it is no longer possible to take the relationship for granted.

Turkey’s military rapprochement with Russia is particularly troubling for Washington. Its insistence that it will go ahead with acquiring a Russian missile-defense system may very well prove a historic mistake with paradigm-shifting consequences. If Ankara goes ahead and takes delivery of the Russian S-400 system, it will not only have to forgo delivery of American F-35 stealth fighter jets, but it will also face severe military sanctions under a US law known as Countering America’s Adversaries Through Sanctions Act (CAATSA).

The S-400 missile-defense system is due to be installed in Turkey in October. But the administration of US President Donald Trump still hopes to change Ankara’s mind with the opportunity, instead, to buy a NATO-compatible missile-defense shield. That said, Turkish President Recep Tayyip Erdogan’s government missed a “soft deadline” in mid-February set by the Americans to decide whether to buy the Patriot missile-defense system. The US offer is contingent upon Turkey canceling its purchase of Russia’s S-400s, and expires with a hard deadline at the end of this month.

Without publicly rejecting the US proposal, Erdogan has repeatedly said he will not pull out of the contract with Moscow. “The deal is done and there is no turning back,” he responded recently when questioned about the contract. “Nobody should ask us to lick up what we spat [out].” In defiance of Washington’s thinly veiled threat of sanctions, Erdogan further pointed out that his country might even seek to procure Russia’s next-generation S-500 system.

The main concern of American policymakers is that Turkey’s operation of F-35 aircraft in range of the S-400s will compromise the advanced technology with which the North Atlantic Treaty Organization’s frontline fighter is equipped. The Russian missile-defense system has a highly advanced radar capable of collecting electronic intelligence. Washington believes the S-400 system can covertly obtain critical information, such as the F-35’s detection range, and relay the data to Moscow.

The Turkish response to American concerns is that Russian technicians will not be allowed to service the S-400s, and that the Russian system will not be plugged into NATO networks. Turkish security officials have also apparently assured their American counterparts that they will redesign the missile-defense system’s operating protocol to prevent any Russian intelligence-gathering.

None of these assurances are convincing to Washington. The Pentagon remains highly concerned that sensitive information will eventually end up in Russian hands, no matter what measures Turkish authorities take. NATO’s supreme allied commander, General Curtis Scaparrotti, recently warned the US Senate Armed Services Committee about Turkey taking delivery of the S-400 in very blunt terms: “My best military advice would be that we don’t follow through with the F-35, because an ally that is working with Russian systems, particularly air-defense systems, is a problem for our most advanced technological capabilities.”

If Turkey insists on the Russian missile defense, the blocked transfer of F-35 jets will only be the first phase of Washington’s retaliation. More significant for the future of the military relations will be the imposition of sanctions that will undermine the entirety of US-Turkish defense cooperation. In other words, myriad Turkish projects that depend on US equipment and cooperation will be impacted with the sanctioning, under CAATSA, of several Turkish aerospace firms.

This looming crisis has paradigm-shifting potential because it clearly shows that the Turkish and US militaries no longer see each other as partners. Beyond defense procurement, the Turkish decision to buy Russian missile defense is symptomatic of a much larger geo-strategic predicament: Washington and Ankara no longer share the same strategic interests and threat perceptions.

In the eyes of Ankara, Washington has partnered with Kurdish terrorists in Syria. And for Washington, Ankara is in bed with jihadist groups in the same country. Syria has turned into a nightmare for Turkish-American relations.

What’s more, both are actively engaged in working against each other. It is one thing to see things differently, but partnering with each other’s rivals has clearly created a radical mental shift in the way the two militaries contemplate each other.

For the United States, there is no bigger threat to the stability of Europe and the future of NATO than Russia. Ankara certainly knows this. But for Turkey’s strongman leader, there is no more ominous a threat to his regime’s survival than Fethullah Gulen – the religious leader Erdogan blames for instigating a failed coup against him – and Kurdish nationalism. Given Gulen’s continued presence in the United States and US support for Syrian Kurds, it is an open secret that Ankara now views Washington as an enemy.

Within this toxic environment, the US and Turkey are walking ever closer to the precipice. The S-400 deal and the cancellation of the F-35s could very well push them over. Instead of parsing the future of the Turkish-American strategic partnership, we may very soon be writing an obituary for their military relations.

This article was provided to Asia Times by Syndication Bureau, which holds copyright.