AP Photo

Foreign policy is rarely decisive in general elections. But it reveals something about the character of a political party and whether its leadership is oriented towards the future or the past.

After the Irish referendum result, a decade of deadening debate over the European Union’s institutional shape is finally coming to an end. Every European government is breathing a sigh of relief. Every mainstream opposition party is looking to the future. Every mainstream opposition party, that is, except the British Conservatives. Because David Cameron is stuck gazing in the rear-view mirror.

The passage of the Lisbon treaty is a massive opportunity for Europe. In the coming decades, as economic and political power shifts eastwards, there is a danger that we could see the...