When David Cameron was elected leader of Britain's Conservative Party, the press called him the "heir to Blair." Like Labour premier Tony Blair, he was a young leader who dragged his sometimes reluctant party toward the political center.
Cameron steps down Wednesday after six years as prime minister — like Blair, defined by a historic blunder.
For Blair, it was the 2003 invasion of Iraq. For Cameron, it was the decision to call a referendum on Britain's European Union membership. He gambled that voters would choose to remain, after a cathartic debate that would resolve Conservative Party divisions on Europe.
Instead, Britain voted by 52 percent to 48...