In a clear signal that medicine and politics make strange bedfellows, a crucial Senate committee on Tuesday, which unanimously approved Dr. Robert M. Califf, a cardiologist and clinical trial expert from Duke University as the commissioner of the Food and Drug Administration, is unlikely to happen soon, because Senator Lisa Murkowski of Alaska has pledged to block his candidacy over the agency’s approval of genetically engineered salmon.

Murkowski, a Republican, said she would put a hold on Califf’s candidacy because the F.D.A. approved a genetically engineered salmon for consumption days after she questioned him on the topic at his confirmation hearing in November. The senator’s state is a major salmon producer.

Even though Murkowski is a member of the Senate committee which approved Califf’s nomination by unanimous voice vote, she voted for Califf because her hold can be placed on his candidacy only after it leaves the committee, she said.