AFAIK, the Nato has a principle called Consensus Decision. When a member wants to join the bloc, it must have the consent of all the countries in the bloc, and when a country is revoked its membership of Nato, it must also have the consent of the whole Nato bloc. Which means that Turkey can only leave NATO if and only if it votes for itself to leave the bloc, the US cannot unilaterally revoke Ankara's membership.
Technically there is no details defined in NATO treaty about reasons and procedures for expulsion of a member state. They have left it wide open and can interpret it anyway they want. Basically they say in case of "material breach of the treaty" the membership can be revoked. And "material breach of the treaty" can mean anything like war crimes committed by Turkey in Syria.
P.S. At least 16 countries in Europe surpassed double digits inflation so far.