Nicknamed "Old Rough and Ready," Zachary Taylor served more than 40 years as a professional soldier on the country's frontiers in Indiana, Louisiana, Minnesota, Wisconsin, Florida, and Texas. In the U.S.-Mexican War, he defeated the Mexican army in a decisive battle at Buena Vista and became a national hero. I lected president in 1848 by the Whig party, Taylor faced the most divisive political issue of the era: should the million square miles of new...