CHICAGO (AP) – Democratic leaders in Cook County hope to rally around a singular candidate to replace former U.S. Rep. Jesse Jackson Jr., because the slate for the primary election is expected to be large.

Jackson, a Chicago Democrat, resigned last week after nearly 17 years in office. He cited his health and acknowledged that he’s under a federal investigation and cooperating with authorities.

The opening is rare in the mostly urban district that covers neighborhoods on Chicago’s South Side, south suburbs and some rural areas.