Prime ministers often have to work with prime ministerial aspirants, senior ministers who regard themselves as possible successors. But can these challengers seize the job when the prime ministers are reluctant to stand down? Using evidence from Canada, Britain and Australia, the article explores the conditions in which successions have taken place and the capacity of the prime ministerial aspirants to expedite the process. It identifies three alternative strategies that are shaped by the party rules in the different countries. The aspirants may flee, fight or fulminate. Which strategy will best improve their chances of winning the top job depends on the traditional or developing modes of leadership election that their parties have adopted. Some processes provide the means to assassinate the leader. Others have no opportunity to act; rivals can do nothing but wait, either in or outside parliament. The article finds that the broader the constituency that elects the leaders, the more secure those leaders are when their reputation declines.