Investigators for special counsel Robert Mueller carried out an early-morning search on the home of former Donald Trump campaign manager Paul Manafort last month. FBI agents seized documents and other materials related to taxes and foreign banking in the unannounced raid. The move, which required a federal magistrate judge to approve a search warrant based on probable cause that evidence of a crime could be found in Manafort’s home, is a sign that the investigation is intensifying, legal experts say. The search also indicates that Manafort may be in a tenuous position with prosecutors.