Mehmet Oz said Wednesday that he would renounce his dual citizenship with Turkey if he’s elected to the U.S. Senate from Pennsylvania, aiming to defuse an issue that has increasingly been the focus of attacks from Republican primary rival David McCormick.

His announcement came shortly after Sen. Dan Sullivan (R., Alaska) spoke to reporters on McCormick’s behalf to raise questions about Oz’s citizenship, and a day after Oz faced questions from journalists about the same subject. It was the latest turn in a brutal primary campaign centered on two ultra-wealthy candidates who are battering each other on TV.

McCormick and his allies have for months sought to undermine Oz, the celebrity surgeon known as “Dr. Oz,” by raising doubts about his loyalties and financial interests because of his dual citizenship and previous service in the Turkish Army.

Oz and McCormick are the GOP front-runners in one of the country’s most crucial Senate campaigns, one that could help decide control of the chamber. Recent polling has shown McCormick vaulting ahead of Oz as his allies hammer the surgeon with a flood of attack ads.

“My dual citizenship has become a distraction in this campaign,” Oz, born in Cleveland to Turkish immigrants, said in a statement. “I maintained it to care for my ailing mother, but after several weeks of discussions with my family, I’m committing that before I am sworn in as the next U.S. Senator for Pennsylvania I will only be a U.S. citizen.”

» READ MORE: Mehmet Oz knows TV. Now his GOP opponents are turning Pennsylvania’s airwaves against him.

An unspoken subtext of the attacks is that Oz would be the first Muslim elected to the Senate, and he’s running in a state that has little history of diversity in its statewide elected officials. Pennsylvania elected its first Black man to statewide political office in 2020, Auditor Timothy DeFoor, and has only ever elected white men to the Senate.

“The bigoted attacks my opponent Dave McCormick has made against me as the child of immigrants are reminiscent of slurs made in the past about Catholics and Jews,” Oz said. “It is a sign of McCormick’s desperate campaign that he has resorted to this disgraceful tactic. It is completely disqualifying behavior for anyone aiming to serve in the United States Senate.”

His decision was first reported by Fox News. The Constitution doesn’t bar dual citizens from serving in Congress. Oz has said he served in the Turkish Army because it’s required to maintain his citizenship.

McCormick allies have said they’re raising legitimate questions about Oz’s loyalties and how he would handle sensitive or classified information if he remains a citizen of a country ruled by strongman Recep Tayyip Erdogan.

» READ MORE: David McCormick’s longtime praise for China and trade could bite his Pa. Senate run

Oz has assailed McCormick’s business ties to China, after McCormick led a hedge fund that invested more than $1 billion there. McCormick’s supporters have pointed to Oz’s potential financial ties in Turkey, including his work as a spokesperson for Turkish Airlines. The Turkish government has a significant stake in the company.

Neither of the candidates has yet had to file his public financial disclosure, which would reveal sources of income and financial assets. They are due next month.

McCormick, an Army veteran and former head of the hedge fund Bridgewater Associates, tweeted Wednesday that Oz should renounce his dual citizenship “now,” accusing his rival of “lying” about his positions on conservative policy priorities.

“Renounce your Turkish citizenship now. We won’t be fooled again,” McCormick tweeted.

McCormick and his allies increased their pressure on Oz on Tuesday, just as Oz held a news conference criticizing McCormick over the huge fees his former hedge fund charged the pension fund for Pennsylvania teachers, while its investments underperformed other benchmarks.

By Wednesday, questions about his citizenship threatened to overshadow the message Oz was trying to drive home.