Turkey's prime minister once spent time in jail for being an alleged Islamist subversive. Now Recep Tayyip Erdogan, until recently one of Europe's most unassailable political leaders, could face more time in the wilderness after suffering a stinging legal rebuff to one of his most cherished policies.

Last week the constitutional court struck down a measure, passed by parliament in February, that would have allowed girls to wear the Muslim headscarf at Turkey's state universities, declaring it a threat to the secular state.