Attorney General Holder testified at a Justice Department oversight hearing. Much of the hearing focused on national security leaks and the government’s “Fast and Furious” operation aimed at arresting members of drug cartels. Committee Republicans said the documents show that senior Justice Department officials knew the operation involved a tactic known as “gun walking,” where smugglers moved guns across the border with Mexico. Mr. Holder said the documents contain no reference to gun walking. He also talked about voting rights enforcement and the Justice Department’s effort to stop a purge of the voter rolls in Florida.