The facts about Bush's service record are not slander by a so-called liberal media. They are documented from FOIA requests, which were the basis for these stories in the mainstream press:
The Boston Globe - 5/23/00
The Washington Post - 6/26/00
The Boston Globe - 7/28/00
The Washington Post - 11/3/00
The bottom line is that between May 1972 and October 1974 he was absent from duty with the Air National Guard. Here are actual scans of relevant documents, obtained from FOIA: Suspended from flying August 1972, "Not Observed" from May 1st, 1972 to April 30th, 1973, and many more.
In fact, rather than a deliberate campaign in the so-called liberal media to tarnish Bush, there has been quite the opposite. CNN actually censored posts from their discussion boards on the topic. George Magazine (run by JFK Jr.) concluded that Bush did accumulate the required number of days for service, but they were using an altered version of Document 99. Here is the original document, unaltered. Using the original (obtained via FOIA), the conclusion drawn by George Magazine is easily refuted. The main error is that George Magazine did not realize that Bush's no-show days were credited to his service record. This is verified by looking at the FOIA-obtained document of Bush's official record.
And the Daily Howler has done an exhaustive analysis using Lexis-Nexis to see if there was any detailed discussion of the topic when the story first broke. There wasn't. The analysis continues in parts two and three.