In Part IV of his series Toward a Field Theory of Journalism Andrew Cline discusses the epistemology of journalism:

… and any answer I offer here is necessarily general and incomplete.
That said, we may observe that journalism operates with an objectivist epistemology: What is real is located in the material world and human actions within that world. What can be known are empirically verifiable phenomena. We are connected to the material world by our senses and certain faculties of the mind, which are capable of perceiving the world through sense impressions and then thinking about, and acting upon, these impressions.
Journalism’s challenge in this epistemology is to perceive the world correctly and then represent perceptions correctly through language.

This also seems to provide a good set of criteria for separating journalism from editorial opinion. While both often appear in the same publication journalism at least attempts the following:

Because it is empirically verifiable that humans disagree about events (our opinions), reporters collect data from “both sides” and present these data without comment, allowing readers to apply their own reasoning to discover the incorrect opinion versus the correct representation of events.

Editorial/opinion content attempts to substitute the writer’s reasoning for that of the reader.
One of our challenges as we apply our own reasoning to journalism is to evaluate the quality of the data being presented and to ascertain whether the data has been inappropriately passed through editorial/opinion based filters.
Yesterday’s post Orchestrating Emergencies suggests that the OMB/White House tend to do the latter rather then provide the citizenry with information that would meet journalistic standards.