I put this question to U.S. Ambassador to NATO Kay Bailey Hutchison this past weekend at the Halifax International Security Forum. Her answer was a definite maybe. She said the Trump administration has made Turkey aware of the ramifications of doing a deal with the Russian defense sector, but the administration hasn't yet decided what to do about it.
"We are going to deal with a tough issue bilaterally, I don't know that a decision has been made on that question. I don't know what the answer will be," Hutchison said.
The Turkish government told the Trump administration it bought the S-400 because it needed something fast, according to Hutchison, and the Turks have promised Washington they won't connect the S-400 to the NATO defense umbrella.
More broadly, I asked her, can Turkey even be a credible NATO ally as it grows closer to the Russian military and acquires systems that directly threaten NATO capabilities?
"Obviously, it's a great concern, there's no doubt about it," Hutchison said. "But on the other hand, Turkey is a very valuable ally in NATO. . . . They have answered the call every time NATO has made a call."
Meanwhile, Defense Secretary Jim Mattis is trying to move forward with U.S.-Turkey defense cooperation despite the possible sanctions. He met with Turkish Defense Minister Nurettin Canikli in Brussels on Nov. 8. After the meeting, Mattis seemed to play down Turkey's missile system purchase from Russia.
"That's a sovereign decision for Turkey," Mattis said. "Clearly, it will not be interoperable with NATO. So they're going to have to consider that if they go forward."
One U.S. official briefed on the meeting said Mattis is trying to secure new U.S. arms sales to Turkey while the administration debates the sanctions issue. One item Mattis and Canikli are discussing is Turkey's purchase of the Large Aircraft Infrared Countermeasures [LAIRCM] system, which protects large planes from getting hit by antiaircraft missiles. The idea is to pitch it to Turkish President Recep Tayyip Erdogan as a means of protecting the planes he flies on, appealing to his fear of another military coup.
The Pentagon declined to comment. But former U.S. ambassador to Turkey Eric Edelman said that Mattis's attempts to woo Erdogan back toward a U.S. friendly position are unlikely to work.
"This is another fool's errand," he said. "It won't succeed because Erdogan has no interest in pursuing this. His interests are served by a bad U.S. relationship. That's why the Turkish government keeps whipping up anti-American sentiment in the press."
Of course, the S-400 is only one of several major irritants in the U.S.-Turkey relationship. Erdogan has jailed a dozen Americans under charges they participated in last year's coup attempt. His officials regularly accuse the United States of supporting terrorists in Syria. His thugs have beaten up peaceful protesters on the streets of Washington.
But the Russian missile purchase is unique because Congress has the power and intention to intervene. Both Republicans and Democrats in Congress are committed to making sure Trump implements the new Russia sanctions, which were levied as punishment for Russia's interference in the U.S. elections.
"I think the administration understands this is actionable," Ben Cardin, Md., the ranking Democrat on the Senate Foreign Relations Committee, told me, referring to Turkey's purchase of the S-400. "Our relationship with Turkey is really getting awful."