They could try not assuming the worst of Trump at every opportunity. Half or more of Trump's "lies" are just extremely uncharitable misinterpretations by reporters desperate for a "shocking" story. Plus they could cut down on opinion pieces disguised as objective reporting.
You are on the money. Trump can whip the media for what is written because everyone knows the bias.
Most media treat him poorly which only reinforces Trump voters' pre-existing views.
With an extremely low bar set on the opinion of Donald Trump, the media will get this wrong when he achieves great things.
Then Trump will bend the media over and do it again.