Turkey's relationship with the U.S. is considered the worst it's been in more than a decade. Turkish President Recep Tayyip Erdogan and Russian President Vladimir Putin both share a general suspicion and mistrust of the U.S., and the two leaders have discussed Moscow selling its S-400 air defense system to Ankara.
Yet another concern is whether Turkey can be trusted since it's scheduled next year to get some of the most advanced U.S. military hardware: Lockheed Martin's F-35 stealth fighter jet.
"Is Turkey, a large and important NATO ally, moving away from NATO and more into the sphere of Russia?" asks Roman Schweizer, a defense analyst at Cowen. "Is that a country that we want to be selling F-35s to? Somebody could ask that question at some point."
To policy analysts, given Turkey would consider the Russian-made S-400 system raises the question whether it can be counted on longer term by the U.S. and NATO alliance. They also suggest the situation highlights the differences over perceived strategic threats by Turkey and NATO as well as the anti-West sentiment after the failed coup a year ago.
"Since the coup attempt, the destabilization is such that you can hardly find a direction that makes sense — at least from a European standpoint," said Marc Pierini, a visiting scholar at the Carnegie Europe think tank and a former European Union ambassador to Turkey. "It goes in all directions at the same time, and this is what is so deeply troubling."
Last week, Russia's new ambassador to Turkey, Alexei Yerkhov, said ties between the two countries are "promising" and closer coordination on Syria "is bringing about very good relations."
There's been a thaw in relations and increased trade that has resulted in Russian wheat now shipping again to Turkey. The Kremlin also plans to launch a joint investment fund with Turkey and to remove trade restrictions.
Later this week, Russia is scheduled to discuss lifting a ban on agricultural imports from Turkey, according to the Tass Russian news agency. Some of the trade restrictions went into effect following Turkey's downing of a Russian warplane near the Turkey-Syria border in 2015.
At the same time, Yerkhov, the Russian ambassador, kept alive reports the Kremlin was preparing to still sell the S-400 air defense system to Turkey and appeared to relish how it's generated concern from the Pentagon and NATO.
"There is a very big murmur both in Washington and in Brussels on this issue," Yerkhov said last week in his first meeting with Turkish media.
The Pentagon and NATO are taking a dim view of the Russian defense system, though, and also worried longer term about ties with Turkey given its home to U.S. warplanes and nuclear gravity bombs at Incirlik Air Base.
"Turkey is a key NATO ally, and we are committed to our strong defense partnership," Pentagon spokesman Johnny Michael told CNBC.
However, the Pentagon official added, "We have relayed our concerns to Turkish officials regarding the potential purchase of the S-400. A NATO interoperable missile defense system remains the best option to defend Turkey from the full range of threats in its region."
Similarly, Turkey in 2015 looked set to be buying China's export version of the FD-2000 long-range air defense missile system for $3.4 billion but backed out after pressure from NATO. Also, the Chinese reportedly refused to budge on all of Turkey's technology transfer demands.
"It could be the case that Turkey is playing what it thinks is kind of a clever game to get the U.S. hardware," said Simon Waldman, co-author of "The New Turkey and Its Discontents."
Added Waldman, "Turkey is still a NATO ally and will continue to be so. But Turkey is increasingly investing in its own kind of military hardware and it wants to be quite independent."
It's still unclear if Moscow and Ankara can agree on price and terms for the S-400, including the transfer of technology and a coproduction arrangement. Turkey, a NATO member since 1952, reportedly sees the technology transfer as a national priority to grow its indigenous defense industry, and U.S. missile defense makers maybe less willing to part with valuable intellectual property.
As for the F-35 stealth fighter jet, Turkey is part of an international consortium that is helping to produce the aircraft, and with that arrangement it will get access to the fifth-generation fighter's technology. Under the current F-35 program, about 10 Turkish companies get to work on the aircraft, ranging from frame structure to production landing gear components. Turkey is scheduled to get 100 F-35 planes.
In July, a group of House members proposed a measure to stop the F-35 sale to Ankara. They cited the May 17 brawl outside the Turkish Embassy in Washington, where Erdogan's Turkish security guards were accused of attacking protesters.
"There is reason to be concerned about the tenor of politics in Turkey," said Steven Cook, senior fellow for Middle East and Africa studies at the Council on Foreign Relations, a Washington think tank. "There certainly is reason to question whether Turkey is an ally. Maybe it's an ally, but not a partner. And I think American policymakers need to keep that in mind."
According to Cook, there is an element within Turkey's nationalists who "very much dislike the West (and the United States). There's believed to be a faction within the security services that are interested in developing relations with the Russians."
A major rift in the U.S.-Turkey relationship is Washington's refusal so far to extradite Islamic cleric Fethullah Gulen, who the Ankara government accuses of masterminding last year's coup. Similarly, Germany has refused to extradite Turks the Erdogan government accuses of involvement in the coup.
Also, Turkey is particularly angry the U.S. is arming YPG-led Syrian Democratic Forces to defeat ISIS. The Kurdish YPG militia (or People's Protection Units) are a branch of the outlawed terrorist group Kurdistan Workers' Party (or PKK).
Violence from the Turkey-PKK conflict has claimed an estimated 45,000 lives since the 1980s.
"I think what we are seeing now is a destabilized leadership in Turkey trying to prove to the rest of the world they have options," said Pierini, the former EU ambassador to Turkey. "They are displeased with the U.S. administration because of its support to YPG."
Experts point out that the U.S.-Turkey relationship may be further challenged in October when the trial is scheduled to start for Reza Zarrab, a Turkish businessman accused of money laundering and bucking sanctions on Iran. There's been speculation Zarrab could testify that some prominent Turkish officials knew of the alleged scheme, including Erdogan or persons in his inner circle.