I think it may be important to distinguish the "journalist"-historians who write books (e.g., Isaacson, Kidder) from the periodical-journalists who write for monthly, weekly, or daily publications. My impression is that the former do years of reading and interviewing of participants (Isaacson in one of the podcasts said he had been collecting material for many years) and the result (while maybe somewhat misguided) is mainly their interpretation (or at least good story); and the latter have a tendency to use less primary sources, interview people who have done research rather than participants, etc., with much more control exerted by editors (as Nathan said). See Kidder's book _Good Prose: The Art of Non-fictioni_ co-authored by his decades-long editor.