Federal investigators have obtained a warrant to begin searching a large cache of emails belonging to a top aide to Hillary Clinton, federal law enforcement officials said Sunday, as prosecutors and F.B.I. agents scrambled to review as much of the information as possible before Election Day. It remains unclear, though, whether they can finish their work by then. “The process has begun,” a federal law enforcement official said.

This month, agents in an unrelated investigation of the disgraced congressman Anthony D. Weiner discovered emails belonging to his estranged wife, Huma Abedin, the aide to Mrs. Clinton. That prompted a renewed interest among F.B.I. agents who had investigated Mrs. Clinton for her use of a private email server as secretary state and had concluded their case without charges in July. READ MORE