(Reuters) - Preliminary analysis has found that a white substance that prompted the evacuation of Hillary Clinton’s campaign headquarters in Brooklyn, New York, was not harmful, police said on Saturday. The substance arrived through the mail at Clinton’s campaign office in Manhattan, and was transported to the headquarters in Brooklyn Heights, police said. The floor was evacuated as a precaution, and several people were exposed to the substance. A New York City Police Department spokesman said police were still investigating the precise nature of the substance, as well as the identity of the sender. 