Republican Dave McCormick, projected winner of the Pennsylvania Senate race, is challenging the state’s process for counting provisional ballots, leading his opponent, who has not conceded, to question the legitimacy of his claimed victory. 

Mr. McCormick is leading three-term Democratic Sen. Robert P. Casey by 0.5 points, a margin that would trigger an automatic recount under state law if it holds. 

The Associated Press called the race for Mr. McCormick on Thursday afternoon, reporting that 99% of the ballots had been counted. On Friday, the outlet retained its call but changed the percentage of ballots counted to 98%.

As of Thursday evening, Pennsylvania Secretary of the Commonwealth Al Schmidt said in a statement that “there are at least 100,000 ballots remaining to be adjudicated, including provisional, military, overseas and Election Day votes.”

Some of those had likely been counted by Friday afternoon, when Mr. McCormick was leading by more than 37,000 votes. 

Despite declaring victory in the race, Mr. McCormick is looking to challenge the counting of some provisional ballots.

Mr. McCormick on Friday filed a petition and complaint in a case challenging 15,000-20,000 provisional ballots the Philadelphia County Board of Elections was set to begin curing on Friday. 

At issue is an effort to oversee the curing process to ensure provisional ballots that are unsigned, do not contain a secrecy envelope or otherwise do not meet the requirements of state law are not counted. 

Mr. McCormick is petitioning the court for a special injunction to permit the provisional ballots to be challenged in groupings where they “share the same deficiency” rather than individually. 

“Plaintiff is concerned that the sheer number of provisional ballots will overwhelm the capacity for individual challenges, creating an impractical burden that risks errors or inconsistencies in the adjudication process,” Mr. McCormick’s attorneys wrote in the petition. “Without the ability to make global challenges, plaintiffs fear that potentially non-compliant ballots may be improperly counted, compromising the fairness and integrity of the election.”

Mr. McCormick’s attorneys cite a “significant disparity in the number of authorized Democratic Party representatives compared to authorized Republican Party representatives” — 38 to 11 — to oversee the curing process as a reason for the court to grant global challenges. 

The petition also requests the provisional ballots cast by voters who had previously requested mail-in or absentee ballots be sequestered pending further action from the Supreme Court in a different case.

In that case, the Republican National Committee intervened in a lawsuit brought against Butler County by voters whose primary provisional ballots were not counted because they lacked a proper envelope and petitioned the Supreme Court to halt the counting of provisional ballots in Pennsylvania’s general election.

The RNC sought to overturn a decision from the Pennsylvania Supreme Court that greenlit the counting of the Butler County ballots if the voter had cast his or her mail-in ballot on time. A provisional ballot is cast if there is a technical issue with a mail-in ballot, such as a lack of signature or date or an envelope error.

The Supreme Court declined to take up the RNC’s petition, noting that the original case pertains to just two ballots in the primary that has long passed, but signaled it may be willing to revisit the issue after the general election. 

Mr. McCormick’s attorneys argued that provisional ballots from voters who had previously requested mail-in or absentee ballots should be sequestered until it is clear whether the Supreme Court will take additional action in the Butler County case. 

“Greater injury would result from allowing these ballots to be adjudicated and counted without sequestration, potentially impacting the election outcome and/or violating statutory requirements,” they wrote in the petition.

Mr. Casey’s campaign and other Democrats seized upon the line that referenced a potential impact on the election outcome, arguing Mr. McCormick’s lawsuit undermines his own claims that he won the Senate race. 

“The party that doesn’t like the outcome, they claim it’s voter fraud. The same party doesn’t want to count every vote, and claim a ‘victory’ in our Senate race,” Pennsylvania Sen. John Fetterman wrote on X. “That party can chill the F out because we are gonna count every last one in PA.”

Mr. Fetterman also complained that the more than 64,000 votes cast for the Green Party candidate helped Mr. McCormick, writing, “Green dips——’ votes helping elect the GOP.”