In 1931, when Franklin Roosevelt was considering whether he should, and could, run for the presidency, he called in three physicians to advise on his physical capability. They reported that the man who had contracted polio ten years earlier, losing all movement in his legs, was indeed in good health—and, furthermore, that he had "no symptoms of impotentia coeundi." "In plain English," writes historian Joseph E. Persico, "he could sustain an erection."

It is a significant detail for Persico, given the questions he seeks to answer in his new book, "Franklin and Lucy: President Roosevelt, Mrs. Rutherfurd, and the Other Remarkable Women in His Life": Did he have an ongoing relationship with Lucy Mercer (later Rutherfurd)? Was it sexual? Was she the only one? His answers to each are yes, undoubtedly, and no.