Front-Runners in G.O.P. Pennsylvania Senate Race Are Put on Spot at Debate

When the leading Republican candidates for Senate in Pennsylvania — the Trump-endorsed celebrity surgeon Dr. Mehmet Oz and David McCormick, a former hedge fund executive — shared a debate stage for the first time on Monday night, they faced sharp attacks not only from each other but also from three other candidates vying to chip away at their polling lead.

With few substantive policy disagreements among the five candidates, attacks instead addressed how long each had lived in Pennsylvania (for Dr. Oz and Mr. McCormick, not much, recently); past commitments to other countries; and Dr. Oz’s statements during the early months of the coronavirus pandemic encouraging people to wear masks — now a verboten position among the Republican faithful.

Dr. Oz rarely failed to remind viewers that he had won an endorsement from former President Donald J. Trump, a victory he used to proclaim himself the true “America First” candidate in the race. His rivals disputed the designation.

“The reason Mehmet keeps talking about President Trump’s endorsement is because he can’t run on his own positions and his own record,” Mr. McCormick said. “The problem, doctor, is there’s no miracle cure for flip-flopping, and Pennsylvanians are seeing right through your phoniness and that’s what you’re dealing with and that’s why you’re not taking off in the polls.”

The latest public polls of the race, when taken together, show Dr. Oz and Mr. McCormick locked in a near tie for the lead ahead of the May 17 primary, a fact that was close to the minds of their rivals Monday.

The three others on stage — Kathy Barnette, a political commentator who has written a book about being Black and conservative; Jeff Bartos, a real estate developer; and Carla Sands, who was Mr. Trump’s ambassador to Denmark — sought to attack the front-runners both individually and as a pair of carpetbaggers trying to buy a Senate seat.

“The two out-of-staters, the two tourists who moved here to run, they don’t know Main Street Pennsylvania,” Mr. Bartos said. “They haven’t cared to spend time there until they decided to run for office.”

The Cleveland-born Dr. Oz, a son of Turkish immigrants who attended the University of Pennsylvania for business and medical schools and who has spent most of his adult life living in New York and New Jersey, recently changed his voting address to his in-laws’ home in the Philadelphia suburbs.

Mr. McCormick, who was born and raised in western Pennsylvania, moved back to the state from Connecticut, where he served as chief executive of Bridgewater Associates, a hedge fund.

The debate also reflected the efforts of the second-tier candidates to make jingoistic appeals while painting Dr. Oz and Mr. McCormick as having loyalties to other nations ahead of the United States. Ms. Sands, who also moved back to Pennsylvania ahead of the Senate race, said neither could be trusted to place America first.

She said that Dr. Oz was “Turkey first,” adding, “He served in the Turkish military, not the U.S. military, and he chose to do that. He chose to put Turkey first.” She said that Mr. McCormick “is China first. He made his fortune in China, and he is China first.”

Dr. Oz defended his stint in the Turkish military as compulsory to maintain his Turkish citizenship, which he said he needed in order to visit his mother in the country. Mr. McCormick said his international business career would be a benefit to decision-making in the Senate.

And Ms. Barnette reflected the other candidates’ attempts to appeal to Trump voters. She even included a rare — for Republican primary circles — critique of the former president.

“MAGA does not belong to President Trump,” she said, using the acronym for Mr. Trump’s campaign slogan, Make America Great Again. “Our values never, never shifted to President Trump’s values. It was President Trump who shifted and aligned with our values.”

The debate demonstrated how a commitment to Mr. Trump serves as the centerpiece for the Oz campaign. He mentioned the former president’s endorsement in nearly all of his responses, and, while Mr. McCormick dodged a question about whether Republicans should “move off 2020” and stop discussing Mr. Trump’s defeat, Dr. Oz said the party must lean into the false claims surrounding the 2020 election.

“We cannot move on,” Dr. Oz said. “There were draconian changes made to our voting laws by Democratic leadership, and they have blocked appropriate reviews of some of those decisions. We have to be serious about what happened in 2020, and we won’t be able to address that until we can really look under the hood.”

Monday’s debate was the first to feature the race’s two front-runners after Dr. Oz and Mr. McCormick skipped a televised debate in February. Both entered the race after the previous Trump-endorsed candidate, Sean Parnell, a former Army Ranger who received the Purple Heart for his service in Afghanistan, dropped out in November after losing a child custody dispute with his estranged wife.

Both Dr. Oz and Mr. McCormick have primarily funded their campaigns themselves. According to the most recent campaign finance reports, $11 million of the $13.4 million Dr. Oz has raised has come from his own pocket. Mr. McCormick has given his campaign $7 million of the $11.3 million he has raised.

For months the two engaged in fierce public and private campaigns to win the affection of Mr. Trump. Mr. Trump this month chose Dr. Oz, playing up his success as a television show host while also being wary of Mr. McCormick’s past business dealings in China.

Pennsylvania Democrats have their own contested primary between John Fetterman, the lieutenant governor and the front-runner; Representative Conor Lamb; and Malcolm Kenyatta, a state representative from Philadelphia.