WASHINGTON (Defense News) – US Senate Majority Whip John Thune, (Republican from South-Dakota) has proposed an amendment to the 2021 National Defense Authorization Act that would allow the purchase to be made using the U.S. Army’s missile procurement account.

The move comes a year after the U.S. expelled NATO ally Turkey from the multinational F-35 program because it received the S-400 in a $2.5 bln deal. Turkey is the first NATO member state to purchase such systems from Russia. The deliveries of S-400 launchers to Turkey began on July 12, 2019.

Meanwhile, Senate Foreign Relations Committee Chairman Jim Risch (Republican from Idaho) has introduced an amendment that would take a tougher stance, mandating the Trump administration implement CAATSA sanctions on Turkey within 30 days of passage of the NDAA. Risch has been critical of Erdogan and accused him of bad faith in dealings with the U.S. over the S-400.

Under CAATSA, or the Countering America’s Adversaries Through Sanctions Act, passed in 2017, any nation procuring a major defence article from Russia should face major sanctions. The sanctions question is important not just for Turkey, but for other partners who may consider Russian gear, says a U.S. State Department official.

U.S. President Donald Trump has held off imposing sanctions against Turkey for its purchase, but the sale remains a sticking point in the relationship. Erdogan has refused to give up the system, despite warnings from Washington that the S-400 could compromise the stealthy F-35.