I AM a genetic Republican. Five generations of Tafts have served our nation as unwaveringly stalwart Republicans, from Alphonso Taft, who served as attorney general in the late 19th century, through William Howard Taft, who not only was the only person to be both president of the United States and chief justice of the United States but also served as the chief civil administrator of the Philippines and secretary of war, to my cousin, Robert Taft, a two-term governor of Ohio. As I write, a photograph of my grandfather, Senator Robert Alphonso Taft, looks across at me from the wall...