Before Nato’s ministerial meeting on Tuesday, the US ambassador to the alliance, Kay Bailey Hutchison, singled out fellow member Turkey for its “problematic behaviour” and operating "out of bounds" in its acquisition of the Russian S-400 missile system. "The idea that you can put a Russian-made missile defence system in the middle of our alliance is out of bounds. We have registered that with Turkey time and again," Ms Hutchison told <em>The National </em> on Monday. Turkey acquired and deployed the Russian S-400 system in July 2019 and has been testing it ever since in defiance of Nato objections and US sanctions. While she called Turkey a Nato long-time ally, Ms Hutchison described the country’s behaviour in the Eastern Mediterranean, the Nagorno-Karabakh conflict and the acquisition of the S-400 as problematic to the alliance. “Some of the behaviour that has been mentioned is problematic to the unity of the alliance and the alliance is strong because we are unified. We are concerned most especially about the S-400,” she said. Turkey has not activated the system yet and the US ambassador is urging Ankara to think twice before doing so, or suffer the consequences. “We hope before Turkey turns on that missile defence system that they will understand the consequences and how much it will hurt their alliance inter-operability with the rest of us.” Ms Hutchison emphasised that it is not too late for Turkey to reverse the transaction with Russia. “We hope that Turkey turns back the decision that they made in error to put a Russian missile defence system in Ankara. Many of us are trying to work with Turkey in a way that would cement our alliance unity and we are asking Turkey once again to be the great ally that they have been in the past,” she said. But Aaron Stein, a Turkey expert and the director of research at the Foreign Policy Research Institute, said it was unlikely that Ankara would reverse its actions in regard to the S-400. "They took ownership of the S-400, sent personnel to Russia for training and then tested the system in Turkey. They can choose to keep it in storage, but that doesn't mean that Caatsa still doesn't apply. That is the conundrum," Mr Stein told <em>The National.</em> Caatsa is the Countering America's Adversaries Through Sanctions Act, passed overwhelmingly by Congress in 2017 to sanction any significant transactions with Russia. In the case of Turkey, outgoing US President Donald Trump has delayed the imposition of Caatsa sanctions on Turkey, but with pressure growing from Congress, president-elect Joe Biden may have little choice. “The Biden administration is inheriting a mess, largely of Turkey and Mr Trump’s own making. The relationship is dysfunctional, but on the S-400 issue, there is a US law that Trump ignored and that Turkey has benefited from ... and issues deferred under Trump will have to be dealt with,” Mr Stein said. The US president-elect has not spoken to Turkish President Recep Tayyip Erdogan yet. “The Biden administration is going to have to make the case for Turkey with a very angry Congress,” Mr Stein said. “Ankara would have to be willing to compromise, but thus far, we have seen no evidence that they are willing to do much.”