On 7 October 2021 the Polish Constitutional Court delivered its judgment in case K3/21, holding that the basic foundations of European integration, such as the primacy of EU law and the EU understanding of judicial independence, were contrary to the Polish Constitution. This paper explores the consequences of the ruling for the European project, with a special emphasis on the principles of mutual trust and mutual recognition in criminal cases. Contrary to what some academics believe, the judgment is short of a notification of intent to withdraw from the EU under Article 50 TEU. But it does have very serious implications beyond the borders of Poland for the common European project, and marks the end of judicial cooperation in the area of freedom, security and justice (AFSJ). EU institutions still try to uphold the semblance that specific judges were independent in the Polish anti-constitutional setting and force member states’ judges to cooperate. But such an approach risks violating fundamental rights, especially the right to a fair trial. This in turn forces national courts to either disregard EU law, or compromise on fundamental rights and get into an open conflict with the European Convention on Human Rights (ECHR). The only way to resolve this tension is to openly acknowledge the end of the era of mutual trust and suspend mutual recognition-based laws.