Is the principle of Mutual Trust a challenge to an effective EU Foreign Policy?

The principle of mutual trust in the process of European integration acquired a major functional role as a principle of governance, a legal principle. As the Court has repeatedly explained, it is based on the "fundamental premise that each Member State shares with all the other Member States, and recognises that they share with it, a set of common values on which the EU is founded", values stated in Article 2 of the Treaty on European Union. Relations between the EU Member States, based on equality and reciprocity, have evolved in the context of European integration into relations based on mutual trust. However, the principle of mutual trust often appears at odds with international commitments and foreign relations of the EU and its Member States. In this paper, I will investigate how a legal principle on which the European integration project is founded represents a challenge to its foreign policy agenda.