Mr. Trump made his first public remarks about the matter on Air Force One as he returned to Washington from White Sulphur Springs, W.Va., where he had held a round table on tax cuts. Asked by a reporter whether he knew about the payment to the actress, Stephanie Clifford, known in her films as Stormy Daniels, he said, “No.”

Asked why Michael D. Cohen, his personal lawyer, had made the payment, Mr. Trump said, “You’ll have to ask Michael.”

The president said he did not know where the money had come from.