The EU's ongoing rule-of-law crisis, entailed by constitutional backsliding in some of its member states, and the fierce debate as to whether and how EU institutions should intervene, have grown into one of the core issues of the European project. Nowadays, it is generally accepted that the rule-of-law predicament undermines the European integration and, sooner or later, a solution needs to be found. But how can there be a rule-of-law crisis in the EU? Rule of law and human rights (hereafter collectively: rule of law) are said to be the fundamental values of Europe (Article 2 of the Treaty on European Union) and the EU has its own detailed bill of rights (EU Charter of Fundamental Rights).

The problem is that EU law has no doctrine of “diagonality”. This term refers to the application of EU rule of law against member states, as opposed to “straight application”, which refers to the application of EU law requirements against EU institutions, as well as the application of national constitutional requirements against member states. EU law contains a comprehensive set of rule-of-law requirements, which have a full application against EU institutions (“straight application”) but only a very limited one against member states. EU rule of law applies to member states when they implement EU law (“paradigm of scope”), however, notwithstanding its substantial spillover effects, this diagonality is false, as here member states act as the agents of the EU (“apparent diagonal application”), contrary to cases, where EU rule of law is applied to member states acting in their own field of operation (“genuine diagonal application”).

The dead end of the European rule-of-law debate

The ongoing rule-of-law crisis in Europe brought to the fore a fundamental contradiction of the EU's legal and institutional architecture. On the one hand, rule of law and human rights are (at least on the level of declaration) at the cornerstones of the EU: they are clearly recognized by the founding treaties, serve as non-negotiable preconditions for accession, and ensure that the various European mechanisms based on mutual trust and recognition are operational and effective. On the other hand, EU law has no doctrine of diagonality and appears to have very limited power when encountering recalcitrant member states who are contemptuous of the EU's fundamental values.