They put too much faith in the staggering unpopularity of Labor, led by Prime Minister Gordon Brown. There seemed to be no bottom to his decline in support. And the party had been in power since 1997, when Tony Blair led what he called “New Labor” to a massive victory over the ruling Conservatives. In 2010, people had grown weary of Labor.

But simply being the opposition party, and nothing more, often minimizes the size of a party’s victory. It’s the easy we’re-not-them approach. Relying on it – and a bad economy, in the British case — a party is prone to neglect the importance of making a strong case for itself.

In the British election, this was one reason Labor was able to turn out its core vote and keep Conservatives from winning a majority. The lesson for Republican, facing an unpopular Democratic Party, is obvious: don’t expect circumstances to win for you. You need to run an aggressive campaign.