Why did the US first refuse to sell Patriot missiles to Turkey, later blocked her buying similar systems from China and now repeating the same blockade for Russian S-400s? - Quora
Turkey Sets Price for Sending Missile Systems to Ukraine
US OKs Potential Sale of Patriot Missile System to Turkey
Turkish S-400 Buy to Stop US from Supplying Patriot Missiles, F-35 Fighters: Local Media
US to pull Patriot missiles from Turkey – DW – 08/16/2015
U.S. Says It Will Remove Patriot Missile Defense From Turkey In October : The Two-Way : NPR
US OKs potential sale of air and missile defense system to Poland -Pentagon : r/EuropeanForum
US to withdraw Patriot missiles from Turkey in October
State Department Oks possible sale for Patriot system to Romania, worth USD 3.9 bln. When is the final decision expected? - The Romania Journal
Lockheed Martin F-35 Lightning II procurement - Wikipedia
MIM-104 Patriot, Military Wiki
Turkey purchased S-400s 'because US didn't sell Patriots'
US OKs Potential Sale of Patriot Missile System to Turkey
U.S. Backs Patriot Missile Sale to Turkey in Breakthrough - Bloomberg