There are "at least" 100,000 votes still outstanding, Secretary of State Al Schmidt said Thursday night. According to Schmidt, that count includes "provisional, military, overseas, and Election Day votes."
"We urge patience as election workers continue to do this important work, especially in contests where the margins are very close," he said.
McCormick filed a lawsuit Friday in Philadelphia, challenging the thousands of provisional ballots that city elections officials began counting earlier in the morning.
As of Friday, McCormick led Casey by approximately 34,000 votes.
The Republican spoke Friday in Pittsburgh for the first time after declaring victory.
"There is no path to Senator Casey overcoming my lead," McCormick said.
McCormick said he is not seeking to reject any of the votes still being counted.
Senator Bob Casey has not conceded yet.
In a statement, Casey's campaign said the race is still too close to call due to the thousands of ballots that still need to be counted.
"The number of provisional ballots expected from areas that favor Senator Casey, like Philadelphia and its suburbs, is further proof that this race is too close to be called. As the McCormick campaign admitted in their own lawsuit this morning, the counting of these ballots could have an 'impact on the outcome of the election.' With more than 100,000 ballots still left to count, we will continue to make sure Pennsylvanians' voices are heard," the Casey campaign said in a statement.
In a statement earlier in the afternoon, Elizabeth Gregory, McCormick communications director, said in a statement, "While votes continue to be counted, any way you slice it, Dave McCormick will be the next United States Senator from Pennsylvania."
Casey, perhaps Pennsylvania's best-known politician and the son of a former two-term governor, is seeking a fourth term after facing what he has called his toughest reelection challenge yet.
Casey, 64, is a stalwart of the state's Democratic Party, having won six statewide elections going back to 1996, including serving as the state's auditor general and treasurer.
McCormick, 59, is making his second run for the Senate after losing narrowly to Dr. Mehmet Oz in 2022's Republican primary. He left his job as CEO of the world's largest hedge fund to run after serving at the highest levels of former President George W. Bush's administration and sitting on Trump's Defense Advisory Board.
The race ran on national themes, from abortion rights to inflation. But it also turned on local ones, too, such as Casey's accusation that McCormick is a rich carpetbagger from Connecticut's ritzy "Gold Coast" - a caricature McCormick helped bring to life by mispronouncing the name of one of Pennsylvania's local beers - trying to buy Pennsylvania's Senate seat.
Casey also attacked McCormick's hedge fund days, accusing him of getting rich at America's expense by investing in Chinese companies that make fentanyl and built Beijing's military.
McCormick, in turn, stressed his seventh-generation roots in Pennsylvania, talked up his high school days wrestling in towns across northern Pennsylvania - a sport that took him to the U.S. military academy at West Point - and his time running online auction house FreeMarkets Inc., which had its name on a skyscraper in Pittsburgh during the tech boom.
Casey, a staunch ally of labor unions and President Joe Biden has campaigned on preserving the middle class, abortion rights, labor rights, and voting rights, calling McCormick and President-elect Donald Trump a threat to all those.
McCormick, in turn, accused Casey of rubber-stamping Biden administration policies on the border, the economy, energy, and national security that he blames for inflation, domestic turmoil, and war. He has attacked Casey as a weak, out-of-touch career politician and a sure bet to fall in line with Vice President Kamala Harris if she had become president.
Should McCormick win, he would be part of the red wave responsible for clinching the U.S. Senate.
David Barrett, a political science professor at Villanova, spoke about the impact of Republicans taking control of the Senate.
"The real bottom line is that a determined president who wants to do things can do those things very likely if he has strong support if he has a House and Senate of his political party," Barrett explained.
He also said he isn't surprised by how close the race is, pointing to polls that predicted this as well as advertising.
"I saw a lot of the advertising by McCormick which really, really savaged Senator Casey, and I had the sense Casey was not sufficiently responding in kind," Barrett said.
The race could lead to a recount if it's decided by half a percentage point or less.