Pa., on Thursday conceded the race for Pennsylvania's Senate seat to his Republican opponent, Dave McCormick. NBC News projected McCormick's win in the hotly contested battleground state race shortly after Casey's concession,

The race has been among the closest in commonwealth history, with the two men separated by approximately a quarter of a percentage point.

Casey's concession comes two weeks after the AP called the race for Republican Dave McCormick and after counties had begun a recount process.