The Turkish government had a weapons system procurement decision to make and it was a simple one at that: Turkey could purchase the Russian SA-21 (S-400 to amateurs) surface-to-air missile system, or remain in the F-35 Lightning II program. Ankara could not have both. The Trump administration made it clear that if Turkey decided to purchase and accept delivery of the SA-21 Growler it would bring about their immediate exclusion from the F-35 program.
Turkey made its choice and took delivery of the first SA-21 missiles and launchers this week. Today the US responded with the announcement that it is removing Turkey from the F-35 program because the “F-35 cannot coexist with a Russian intelligence collection platform that will be used to learn about its advanced capabilities”.
Turkish President Erdogan had long assumed the Trump administration would relent and allow his nation to possess both the SA-21 system, and F-35 fighter planes. He was wrong, and now his country is on the outside looking in with regards to the US program.