Turkey currently has military personnel in Russia learning how to operate the new surface-to-air missile system it says will be delivered next month. In the United States, Turkish pilots are training on the F-35 fighter jets their government has ordered from Lockheed Martin.

Washington has made clear to Ankara that if it continues trying to play both sides by going through with the delivery of the Russian S-400, Turkish pilots will leave the US and the F-35s will stay home.

So far, the Turkish government isn't blinking. Foreign Minister Mevlut Cavusoglu repeated Friday that the agreement is going through. "We have no hostility against anyone but we are not living in a rose garden," Cavusoglu said in a news conference. "Our neighbors are not Mexico and Canada like America's neighbors. There have been serious threats in our region and we need to take necessary steps for Turkey's interests."

As for the US threats of possible sanctions, the foreign minister said: "We will certainly respond."

Do trainers in Turkey pose a threat?

NATO observers say there's a much bigger threat with regard to this deal than the admittedly genuine concerns about Russian personnel possibly siphoning off Western secrets during their S-400 training sessions once in Turkey. "The implications are both military and political," former US Ambassador to NATO Doug Lute told DW. "Turkey has slipped farther and faster from NATO's core values — democracy, individual liberty and the rule of law — than any other NATO member. We see again that when states drift from core values the door opens for Russian influence."

Russian President Putin and Turkish President Erdogan clinched a deal that's riled the NATO alliance

But in Turkey's case, the door was opened by Ankara itself. Cavusoglu raised plenty of eyebrows at NATO's 70th anniversary celebrations in Washington in April with his candid remarks saying his country balances its relations with "everybody," which he said caused no contradictions. "Turkey doesn't have to choose between Russia or any others," he said at a public event. "We don't see our relations with Russia as an alternative to our relations with others and nobody, neither West nor Russia, should or can ask us to choose between."

Turkey: We don't have to choose

Vago Muradian, editor-in-chief of the Defense & Aerospace Report, was in the room when those remarks were made and he says there was a palpable ripple of surprise. The stark comments laid bare the bigger issues about where Turkey's loyalty lies in an alliance founded on mutual defense, Muradian says. "That is a far bigger question than just whether Ankara wants to have its S-400s and eat its F-35 cake," he warns. "At the end of the day it's about the reliability of a nation that's been seen as a key part of the NATO alliance throughout the Cold War and the post-Cold War era and now as we reenter an era of great power competition, that's the question I think everybody's focused on."

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Some observers believe the Turkish government has already answered such queries. "What kind of NATO member is this," asks Martens Centre Deputy Director Roland Freudenstein, "if they have to balance between their existing alliance and a hostile power which has proven many times, especially since 2014, its aggressive intentions? To me that's a no-brainer. The very fact that Turkey claims that it has to somehow 'balance' between those two means that it's not a full ally anymore."

Turkey may have to leave its F-35s behind if it doesn't cave to US demands

No compromise in sight

Jim Phillips, senior research fellow for Middle Eastern affairs at The Heritage Foundation, told DW Turkey has the most to lose in the game of "chicken" that will play out between now and the July 31 deadline set by US Defense Secretary Patrick Shanahan. And Phillips doesn't believe Washington will be the one to swerve.

"The US has to stand by its present position," Phillips says. "I don't think it should make compromises on its own security with a Turkish leader determined to pull Turkey away from the West."

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While it's better for NATO overall that Turkey has fighter jets of an F-35 quality, he says, it's just not worth the vulnerabilities it would entail under the circumstances.

The US has already excluded Turkey from participating in multilateral meetings about the F-35 program. However, after a Thursday phone call, Shanahan and Turkish Defense Minister Hulusi Akar announced they'll meet face-to-face at the NATO defense ministers' meeting in late June.