On August 2nd 2017 U.S. President Donald Trump signed the Countering America’s Adversaries Through Sanctions Act (CAATSA) into law, which paved the way for direct action to be taken against parties with military relations with Iran, Russia or North Korea. The U.S. has since undertaken an extensive effort to undermine Russian arms exports, and according to the State Department has pressured a number of parties to abandon plans to acquire Russian weapons.&nbsp;In March 2017 a group of U.S. lawmakers led by senator Bob Menendez told the State Department in a latter than any sale of Russia's S-400 air defence system in particular should lead to new punitive measures including sanctions under&nbsp;CAATSA. The lawmakers stated: "We are writing today to specifically inquire about reported negotiations between Russia and certain countries over sales of the Russian government's S-400 air defence system and whether these reported deals could trigger mandatory CAATSA sanctions.... under any circumstance, an S-400 sale would be considered a 'significant transaction' and we expect that any sale would result in designations." Talks were reportedly being held with Saudi Arabia, Qatar, China, India and Turkey regarding potential repercussions of their acquisition of the Russian air defence system.The proliferation of Russian air defences poses a significant threat to the Western bloc's ability to project power globally, and the use of CAATSA to limit sales of the S-400 represents an attempt by the United States to prevent this while also stripping Russia of a key source of income. Turkey, as a NATO member rather than non aligned third party, has come under particular scrutiny for its plans to acquire Russian air defences rather than those of a Western supplier.&nbsp;Since Turkey confirmed its intention to acquire of a Russian S-400 air defence system, the country has repeatedly be threatened by both the United States and the wider Western bloc with repercussions should it go ahead with the purchase. Washington&nbsp;has indicated that Ankara could come under sanctions, while there have been signs that Turkey could see its arms contracts with the U.S. cancelled - with the F-35 fifth generation fighter being a key weapons system which could potentially be denied to the country. This has come at a time when a number of longstanding Western partners are looking to Russian arms, particularly in the Middle East and Arab world, which seriously threatens the Western bloc's longstanding regional dominance. Morocco, Saudi Arabia and Qatar are all set to purchase the S-400 while Bahrain and Iraq are currently considering such acquisitions for their own air defences. As a client with somewhat less autonomy which is more reliant than others on U.S. assistance to wage its ongoing civil war, Iraq has among the Arab states notably been singled out alongside Turkey and come under significant pressure to abandon plans to acquire the S-400.Amid growing pressure to cancel plans to acquire the S-400, Turkey requested in early 2018 that Moscow alter the schedule for delivery of the S-400 to provide the systems at an earlier date. The delivery of the first complexes are scheduled to be delivered in early 2020. Turkish Foreign Minister Mevlut Cavusoglu stated in March regarding his country's right procure arms independently regardless of the opposition of the Western bloc and the United States: ""Turkey is a NATO member, but we are an independent state, we are not a satellite state." He stated regarding his country's readiness to respond to U.S. or Western sanctions on his country: "If it (the U.S.) wants to punish Turkey with sanctions, Turkey will react in another way, not like Russia or other states... We will respond. You cannot threaten us. The United States threatens many countries saying 'Do not buy gas of one or another country.' That does not work.'" Ultimately whether Washington will risk further damaging relations with its longstanding defence partner by sanctioning Ankara in order to demonstrate its resolve to punish Russian arms importers remains to be seen. Whichever path the U.S. chooses there remain several significant risks - namely that if Turkey is seen to acquire the S-400 without repercussions it will seriously undermine the U.S. and Western effort to undercut Russian arms exports worldwide and make successful pressure on India, Saudi Arabia or other states unlikely.