WASHINGTON — Attorney General Eric H. Holder Jr. announced on Thursday that the Justice Department would ask a court to require Texas to get permission from the federal government before making voting changes in that state. The move opens a new chapter in the political struggle over election rules after the Supreme Court struck down a portion of the Voting Rights Act last month. In a speech before the National Urban League in Philadelphia, Mr. Holder also indicated that the filing, expected later on Thursday, was most likely just an opening salvo in a new Obama administration strategy to try...