Singel served as the state's acting governor from June 14, 1993 to December 13, 1993, during Casey's lengthy battle with amyloidosis and subsequent multiple organ transplant.

During his second term, Governor Casey was diagnosed with Appalachian familial amyloidosis, a rare and usually fatal liver disorder.

Singel sought and lost the Democratic senatorial nomination in 1992 to Lynn Yeakel, who went on to narrowly lose the general election to incumbent Arlen Specter.

Casey declined to either campaign or raise money for Singel's candidacy – an incident that reportedly caused a deep rift between the two men.

He briefly considered running against Senator Rick Santorum in 2000, but withdrew his name from consideration and backed eventual nominee, Pittsburgh-area Congressman Ron Klink.

In 2000, Singel joined the Philadelphia-based law firm Duane Morris as lobbyist and director of its Johnstown, Pennsylvania, branch office.

Singel started his own firm, The Winter Group, in 2005 and continues to practice government affairs today in downtown Harrisburg.