David McCormick Concedes to Dr. Oz in the G.O.P. Primary for Senate in Pennsylvania

David McCormick, a former hedge fund executive, conceded the exceedingly close race for the Republican nomination for Senate in Pennsylvania on Friday to Dr. Mehmet Oz, the celebrity television physician, with a statewide recount underway and no official race call.

Dr. Oz had a lead of fewer than 1,000 votes, or .07 percent, before the county-by-county recount began last week. The unexpected early concession was confirmed by Mr. McCormick’s campaign, five days before the recount’s full results were to be released. It was a recognition that Mr. McCormick had gained only handfuls of votes so far and faced an insurmountable hurdle in making up his deficit.

His decision sets up one of the most pivotal contests of the midterms, a November election between Dr. Oz and the Democratic nominee, Lt. Gov. John Fetterman.

The primary initially produced a photo finish in which both campaigns called for every vote to be counted — a contrast with how Republican supporters of former President Donald J. Trump reacted to his loss in Pennsylvania in 2020.

Mr. Trump, who endorsed Dr. Oz, urged him the day after the election to follow his own conspiratorial script and declare victory before every vote was counted, including absentee and mail ballots trickling in from military and overseas voters.

Dr. Oz, the longtime host of “The Dr. Oz Show” on daytime television, mostly ignored the advice. But as the recount began on May 27, he declared himself the “presumptive” nominee. The recount was ordered by Leigh M. Chapman, the state’s acting secretary of the commonwealth, and was triggered automatically by Pennsylvania law because the gap between candidates was under 0.5 percent.

Armies of lawyers for the candidates challenged small batches of provisional ballots in front of county election boards, sought hand recounts in certain precincts and went to court, scrapping over every vote. Mr. McCormick, who led his opponent on mail ballots, sued to include 850 or so mail-in votes that were received on time but did not have voters’ handwritten dates on the envelopes, as required by state law.

Both the Pennsylvania Republican Party and the Republican National Committee intervened to oppose the suit. The Commonwealth Court of Pennsylvania sided with Mr. McCormick in granting a temporary order for counties to segregate and count the ballots, providing both a vote tally that includes them and another that does not.

The November election holds high stakes for both parties: Pennsylvania is probably Democrats’ best chance to add a seat to their fragile 50-50 control of the Senate, in which Vice President Kamala Harris holds the tiebreaking vote. With Senator Patrick J. Toomey retiring, the seat is the only G.O.P.-held open Senate seat in a state that Joseph R. Biden Jr. won in 2020. For Republicans, retaining it would ease their path to a Senate majority in a year when the political climate is strongly in their favor.

Dr. Oz, 61, who won Mr. Trump’s endorsement in large part because of his television charisma, was never fully embraced by core Trump supporters, as evidenced by the closeness of the race. At a rally Mr. Trump held in Pennsylvania 11 days before Election Day, boos greeted the mention of Dr. Oz’s name.

Mr. McCormick, a West Point graduate and the former chief executive of Bridgewater Associates, the world’s largest hedge fund, was more competitive than polls and many political experts had expected. In part that was because of Dr. Oz’s history of espousing liberal views, notably on abortion and transgender issues, which made him toxic to some conservatives.

Hesitance to embrace Dr. Oz by the Trump-centric base allowed a late surge by a hard-right candidate, Kathy Barnette. On Election Day, when she finished third with about 25 percent of the votes, she appeared to have siphoned grass-roots Trump supporters from Dr. Oz. She did so after declaring “MAGA does not belong to President Trump,” and despite Mr. Trump’s dismissal that Ms. Barnette, who has a history of homophobic and anti-Muslim remarks, “will never be able to win the general election.”

Dr. Oz and Mr. McCormick, both first-time candidates, worked hard to transform themselves from members of the East Coast elite, with middle-of-the-road politics, into credible champions of the MAGA movement.

Blake Hounshell contributed reporting.