What Happened: In a letter to Turkish Defense Minister Hulusi Akar, acting Defense Secretary Patrick Shanahan gave Turkey until July 31 to discontinue its purchase of the S-400 system or the United States will stop training Turkish pilots on the F-35, proceed with the F-35 development program without Turkish input, and find new manufacturers for jet parts solely made in Turkey. Turkish officials told Hurriyet Daily News that there would be no change in the acquisition of the S-400 in response to the letter. The U.S. "wind down" could take place in early 2020 should Turkey proceed with the S-400 purchase.
Why it Matters: Ending Turkey's involvement in the F-35 would represent a notable breach between the NATO allies and would impact Turkey's manufacturing sector just as the Turkish economy needs growth. The July deadline may also herald a new phase in tensions over the S-400 that could lead the way to U.S. sanctions on Turkey.
Background: U.S. protests over the S-400 have been ongoing for some time, but U.S. officials are now indicating they will take concrete steps to end Turkey's involvement in the F-35 program, a weapons system built with many of America's key allies, as retaliation for Ankara's purchase of the S-400, which U.S. officials worry will cause the F-35's technological secrets to be leaked. Congress is also preparing legislation to block the sale of the F-35 to Turkey, potentially negating any deal that might come from direct talks between U.S. President Donald Trump and Turkish President Recep Tayyip Erdogan at the G-20 leaders' summit or elsewhere.
Why Turkey and the United States Can't Get Along (June 20, 2018)