This could get really ugly, really fast.
Trump as a salesman believed with some reason that the only bad publicity was no publicity. That approach carried him through the primaries because his strongest supporters viewed negative comments from the MSM as a badge of honor. It isn’t working with a general election audience, and it definitely wouldn’t work with him as President.
Trump is notoriously thin-skinned and pugnacious. He bashes the MSM on a daily basis, and bans prominent journalists from his campaign events. There is no reason to believe that this situation would improve if he takes office. You can anticipate that he would threaten libel actions on a regular basis, refuse to communicate with large segments of the MSM, call on his supporters through Twitter to harass reporters he particularly dislikes, and use his regulatory authority in every way possible to deal with journalists and media he views as his enemies.
Think Richard Nixon levels of animosity, only worse.