PHILADELPHIA, Pennsylvania (CNN) -- Sen. Barack Obama in a speech Tuesday addressed the controversy surrounding his former minister, using it as an opportunity to challenge Americans to take a closer look at race relations. Speaking to supporters at Philadelphia's National Constitution Center, the Democratic presidential candidate said he rejected racially charged comments made by the Rev. Jeremiah Wright, but he tried to explain the root of those remarks. Wright formerly preached at Trinity United Church of Christ in Chicago, where the senator from Illinois worships. Some of Wright's old sermons came under fire after an ABC News report last week,...