Frank - Vietnam War is the right time frame. When the MSM forced the impeachment of Nixon on trivial charges - they realized they could make or change the process rather than report it. However, consider these two events in that time frame to gauge the magnitude of their bias:
1969 Ted Kennedy driving drunk, runs off bridge with woman (not his wife), and leaves her to drown. MSM barely reports it - no repercussions for Teddy boy (can you spell cover up?).
1972 Low level operatives attempt to steal Democrat political strategy. Press reacts like German Shepard with a bone in it's mouth and continues with unrelenting reporting until they destroy RMN and his Presidency.