HARRISBURG, Pa. (AP) — With just 910 votes separating the two leading candidates in Pennsylvania’s Republican primary for U.S. Senate, counties were preparing Thursday to start the recount between celebrity heart surgeon Dr. Mehmet Oz and former hedge fund CEO David McCormick.

At least seven counties — Bedford, Clinton, Crawford, Lehigh, Montour, Tioga and Warren — said they will begin Friday, while most other counties said they will begin next week. The initial result from last week’s election remained elusive Thursday, since some counties were still tallying up thousands of remaining ballots.

Oz, who is endorsed by former President Donald Trump, leads McCormick by just 0.07 percentage points out of more than 1.3 million ballots reported by the state Thursday. McCormick’s campaign has scrounged for votes in order to close the gap with Oz, waging a legal effort in state courts to force counties to count certain mail-in ballots that might otherwise get thrown out on a technicality.

In a recount, most of the ballots are simply rescanned electronically. Election workers check ballots by hand if a scanner recorded no vote or dismissed it as a double vote, and they may find more voters there, election lawyers say.

The biggest change in votes could come from the discovery of a data entry error, a human mistake that could go in either direction, they say.

The recount will drag out the official result in the Republican primary until June 8.

The winner of the GOP race will take on the Democratic nominee, Lt. Gov. John Fetterman, in November’s midterm contest. Democrats see it as their best opportunity to pick up a seat in the closely divided Senate. The incumbent, Republican Sen. Pat Toomey, is retiring after serving two terms.

The separation between Oz and McCormick is inside the 0.5% margin needed to trigger a recount under Pennsylvania law, and the state's top election official ordered the recount Wednesday. The Associated Press will not declare a winner in the race until the recount is complete.

The deadline for counties to report their unofficial results to the state elections office was Tuesday. Even so, counties continued counting thousands of ballots on Thursday, including provisional, military and overseas absentee ballots.

Counties have until June 7 to finish a recount and another day to report results to the state.

Court decisions could affect the outcome.

McCormick's campaign has asked the Pennsylvania Supreme Court to order counties to obey a federal appeals court decision and count mail-in ballots that lacked a handwritten date on the outer envelope. A lower court has ordered a hearing next Tuesday on the matter.

Oz, the Republican National Committee and the state Republican Party oppose McCormick’s request. A separate case that affects those same ballots could go to the U.S. Supreme Court.

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Follow Marc Levy on Twitter at twitter.com/timelywriter.

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Follow AP for full coverage of the midterms at apnews.com/hub/2022-midterm-elections and on Twitter at twitter.com/ap_politics.

Marc Levy And Mark Scolforo, The Associated Press