STOCKHOLM — Sweden may be known for its popular music, IKEA and a generous welfare state. It is also increasingly associated with a rising number of Islamic State recruits, bombings and hand grenade attacks. In a period of two weeks earlier this year, five explosions took place in the country. It’s not unusual these days — Swedes have grown accustomed to headlines of violent crime, witness intimidation and gangland executions. In a country long renowned for its safety, voters cite “law and order” as the most important issue ahead of the general election in September. The topic of crime is...