You’d think with a four-hour documentary, there wouldn’t be much on the cutting room floor. But the producers of The Presidents’ Gatekeepers had 90 hours of footage to cull, and they likened the editing process to using a meat cleaver. In a way it shows — the opening scenes of this ambitious documentary jump around among the 20 living chiefs of staff interviewed irrespective of when they served and without a narrative timeline that seems to make sense.