Boyko Borissov, an earthy former bodyguard and mayor of Sofia, is on Tuesday settling into his first full day as Bulgaria’s prime minister. He will need all his pugnacity to defeat his country’s most persistent enemy: corruption.

Bulgarians were embarrassed by a strongly worded EU report last week slamming a “lack of initiative in law enforcement” and condemning the criminal justice system as slow, inequitable and open to interference. Criticism that Bulgaria’s leadership has done too little to end a culture of impunity hits a nerve.