Less than a month ago, our esteemed host noted the manner in which the establishment media serves as potential kingmakers, while operating under the cover of “objectivity.”  New studies now quantify the phenomenon.

The latest report (.pdf) from the Center for Media and Public Affairs from December 16, 2007 through February 19, 2008, found:

Since mid-December, five out of six on-air evaluations of Senator Obama (84%) have been positive, while Senator Clinton’s coverage has been about evenly balanced (53% positive). Since Super Tuesday, however, Obama’s proportion of good press has dropped to 67%, his worst performance during any phase of the campaign, while Clinton’s coverage remained balanced (50% positive). For example, from the South Carolina primary (Jan 26) to Super Tuesday, a remarkable 96% of comments about Obama were positive.

Obviously, not all of that is attributable to a pro-Obama bias.  For example, positive coverage after Obama’s win in South Carolina is to be expected.  However, 96% positive coverage is a level probably not seen since Pres. Bush in the immediate aftermath of the 9/11 attacks.  Moreover, there may well be a feedback loop that develops — glowing coverage boosts Obama in the polls, resulting in positive horse race coverage, etc.  Furthermore, a net-by-net break down of the coverage is revealing:

Senator Obama has received 90% positive evaluations on both ABC and CBS, along with 73% positive comments on NBC.  Senator Clinton’s coverage has varied more across the networks, ranging from 68% favorable comments on ABC to only 38% favorable on NBC, along with 50% favorable comments on CBS.  Thus, the spread between the two candidates is greatest on CBS – a forty percentage point difference in proportion of good press.

The fact neither Obama nor Clinton gets a roughly similar level of positive coverage across networks demonstrates the subjectivity in the reportorial and editorial judgments made with regard to each candidate.  The best example of this is the thirty-point gap in positive coverage of Clinton between ABC and NBC.

Since Super Tuesday, Obama’s positive coverage has dropped to 67% — but that is still higher than Clinton’s 50% positive coverage.  Moreover, during this period, “98% of comments about Sen. Obama’s prospects for winning the Democratic nomination have been optimistic, compared to only 53% optimistic comments on Sen. Clinton’s prospects.”

On the other side of the aisle, John McCain got 97% positive coverage before the New Hampshire primary, but 30% positive coverage since.

Meanwhile, the latest Campaign Coverage Index from the Project for Excellence in Journalism supports the general perception that press scrutiny of Obama became significant only in the past week, as it is at most a sidebar in PEJ’s report for Feb 18-24.

The PEJ reports also include graphs showing the volume of coverage for each candidate over time.  As might be expected, the volume of coverage of McCain has trended downward since Super Tuesday, while coverage of the Democratic race soared.  Again, this is not in itself evidence of a partricular bias as much as a reflection of a consensus that McCain had become the prohibitive favorite to win the GOP nomination, while the Clinton-Obama tussle remained competitive.  However, the gap in coverage is rapidly turning into a chasm.  Moreover, as with the establishment media coverage of the early years of the Iraq mission, reducing coverage to a trickle that remains overwhelmingly negative has a tendency to cement a negative image in the public mind.