Many consumers of the news have their own standard of journalistic ethics and possible news bias; disclose it. For most editorialists, party, issue or candidate affiliation is usually not the issue. In fact, these men and women are opinion writers and there are few who would deny that. The readers may dislike what is being said, may be opposed to the supported issue, candidate or political position, but comments made by the readers and listeners usually acknowledge the real bias.
The news consumer also understands, or should understand, that each news service may look at reporting the same issue or candidate from a different direction. This may appear prejudice, and sometimes it is, but more often it represents reporting from a particular view point to appease the audience demographics, which include the politics of the audience. It is a reason why Fox and MSNBC cater to such different audiences.
There also remains a pervasive belief if it is one the radio, television, Internet or in print, it must be true, especially if that source has the same values. (See above.) And if the report is saying something contrary to our own belief, then the reporter is partisan, leaning toward the opposing political position. Maybe, but most likely not.