As political acts go, an assassination is more like a natural disaster than a controlled explosion: it will wreak havoc, it will often change the course of history, but its perpetrators can never know in what direction. When Gavrilo Princip shot Archduke Franz Ferdinand, in 1914, his objective was South Slavic independence from the Austro-Hungarian Empire; what he got was the First World War and the slaughter of millions. On the other hand, in 1995, when a far-right extremist assassinated the Israeli Prime Minister Yitzhak Rabin, at a rally in support of the Oslo peace accords, he could be said...