Barack Obama is preparing to deliver a major address Tuesday on race, politics and unifying the country after being hounded by questions about his relationship to a pastor whose sermons have been laced with anti-American invective. In a speech whose religious significance could compare to one given in December by former GOP presidential hopeful and Mormon Mitt Romney, Obama may be forced to explain the philosophy of the 8,000-strong Trinity United Church of Christ in Chicago, where the Democratic presidential candidate has been a congregant for 20 years. In announcing the morning address, to be delivered in Philadelphia, Obama would...