It's no secret that Republican-primary voters in Illinois have been almost rigidly hierarchical when it comes to choosing gubernatorial candidates. They pretty much always choose the candidate who can best demonstrate that it's his or her "turn."
In 1990, after eight years as secretary of state, Jim Edgar was the clear choice. Indeed, he barely had opposition. The same went for two-term Secretary of State George Ryan eight years later. In 2002, it was clearly Attorney General Jim Ryan's turn, and he bested two other high-profile candidates in the primary. In 2006, Treasurer Judy Baar Topinka beat three lesser-known opponents to win her primary race, although it wasn't as easy.