Election victories in Britain and Canada show the Labor Party where more work is needed

Voters in Britain gave election watchers a shock in May. Not because David Cameron survived as prime minister – despite the post-election rewrites, a Labour victory hadn’t been widely expected. No, the jolt came because the Conservatives won an absolute majority in the House of Commons. The almost universal expectation, fed by the polls, was that one of the major parties would wind up leading a minority government.

Why were the polls so wrong? Perhaps it was the “shy Tory” effect – the possibility that respondents were bashful about admitting to pollsters that they intended voting Conservative. Or perhaps it came down to the wrong assumptions about which groups would turn out to vote in Britain’s non-compulsory system...