Seven months after taking office, Attorney General Eric H. Holder Jr. is reshaping the Justice Department’s Civil Rights Division by pushing it back into some of the most important areas of American political life, including voting rights, housing, employment, bank lending practices and redistricting after the 2010 census. As part of this shift, the Obama administration is planning a major revival of high-impact civil rights enforcement against policies, in areas ranging from housing to hiring, where statistics show that minorities fare disproportionately poorly. President George W. Bush’s appointees had discouraged such tactics, preferring to focus on individual cases in which...