Republican David McCormick cut into Democratic Sen. Bob Casey's support in Philadelphia and its populous suburbs and built leads in the more GOP-leaning parts of the state, foreclosing the incumbent's pathway to victory when The Associated Press called the race Thursday.

A small margin in votes separating incumbent Democratic Sen. Bob Casey from Republican challenger David McCormick Jr. has triggered a recount in the Pennsylvania Senate race, the commonwealth's secretary said Wednesday.

Republican Dave McCormick leads Democratic Sen. Bob Casey by about 28,000 votes, under the 0.5-percentage-point threshold for an automatic recount under state law.