We examine whether judicial review can affect nation building by studying how the ruling of the Spanish Constitutional Court on the Catalan Constitution affected Catalan support of secession, which doubled in the 2010-2012 period. Our identification strategy relies on the fact that the ruling occurred amidst a public opinion survey. We find that the ruling led to a 20\% increase in support for Catalan independence from Spain in 2010. In terms of mechanisms, we show that the ruling decreased identification with the Spanish national identity and trust in national institutions. We find that the ruling increased the intention to vote for Catalan nationalist parties and is associated with a long-lasting increase in electoral polarization in Catalonia.