"I just called Dave McCormick to congratulate him on his election to represent Pennsylvania in the United States Senate," Casey said in a statement Thursday. "As the first count of ballots is completed, Pennsylvanians can move forward with the knowledge that their voices were heard, whether their vote was the first to be counted or the last."
Voters were being tallied this week because the election vote totals fell within the 0.5% margin. A recount was mandatory under state law.
As of Thursday, McCormick led by about 16,000 votes out of almost 7 million ballots counted.
"Senator Bob Casey dedicated his career to bettering our commonwealth. Dina and I want to extend our sincere gratitude to Senator Casey, Terese, and their family for their decades of service, hard work, and personal sacrifice," said McCormick in a statement.
Casey, perhaps Pennsylvania's best-known politician and the son of a former two-term governor, was seeking a fourth term after facing what he has called his toughest reelection challenge yet. He was first elected in 2007.
This was McCormick's second run for the Senate after losing narrowly to Dr. Mehmet Oz in 2022's Republican primary.
Republicans will have a 53-47 majority next year in the U.S. Senate.