Spain has had a caretaking administration for ten months and has formed an unstable minority government in October; meanwhile, Catalonia remains on track for secession.

The battle now is turning into a confrontation between the Spanish rule of law and the Catalan secessionist movement. Spain’s Constitutional Court could test the limits of the Catalan secessionist resolve by prosecuting the movement’s leadership.

Paradoxically, it could also favour the Catalan secessionist movement by alien...