The Leave campaign was right to pour scorn on David Cameron’s warning this week that Brexit could threaten Europe’s military stability and lead to war. Boris Johnson mocks the Prime Minister about his prophecy on page 14. If Cameron really believed that Britain leaving the EU could lead to war in Europe, why on earth did he risk having a referendum at all? Why was he suggesting until a few weeks before his negotiations with EU leaders that he would consider voting for Brexit if he didn’t get his way?

It’s easy to tease the increasingly shrill alarmism of the Remain...