A nice history lesson here from Chris Briem on the effects of the county's resign-to-run requirements on its council (with a nod to now-DJ Gene Ricciardi, the city council president before Luke Ravenstahl):

With news of another entrant to the race for Allegheny County Executive, it looks like Rich Fitzgerald will be announcing his candidacy today.  Though others are looking to overturn the rule, County Council rules currently require a sitting member to resign in order to run for another office.  Remember Jim Simms' bid for County Controller where he also had to give up his role as County Council president to run for county controller.  The story was he supposedly had some solid support to back him, but Flaherty snuck in and wrested the ACDC endorsement from him even. So that support must not have really been there and Simms' tenure as the most powerful African American in (the history of?) county politics was cut short by the rule that disallowed incumbents to simultaneously run for other political offices.  One could muse over the counterfactual that if he had become controller, he would be in the pole position for ACE now. Him and Mayor Ricciardi I suppose.