Before the election results were announced, Ken Livingston offered jobs to his three main rivals. His losing the election shows us why he did that. It's easy to make the offer, the electorate think you're being reasonable.
But, if you take the job, then you can't really campaign against your employer at the next election. It's said that you can't win elections, you can only lose them by doing a bad job. Well, in that event, poor performance reflects on the whole team. So, in this example, Ken was invited back into the Labour party a few years ago. He accepted that invitation, and Gordon Brown's cock-ups have reflected on Ken.