Former President Donald Trump's request for appointment of a third-party Special Master to review documents seized from Mar-a-Lago shines light on the role that government filter teams play in criminal investigations.  While the search of Mar-a-Lago was extraordinary in many respects, the creation of a "filter team" with protocols approved by a magistrate judge was routine. Taking away the bombastic rhetoric in his filing, Mr. Trump's stated concern about the prosecution team having access to privileged materials is also typical.