US presidential election campaigns have always been a season of mudslinging. But this year's contest has been marked by the narrow focus on the Vietnam era military records of President George W. Bush and his Democratic rival, Senator John Kerry, and the wide array of media through which battle on this issue has been fought - in TV advertisements, on websites and the internet. Now, however, a pillar of American broadcasting has got caught up in this partisan affray, and been badly compromised as a result.

CBS News has had to apologise for using questionable documents to challenge Mr Bush's service in the National Guard in the early 1970s. This came after CBS spent two weeks first stoutly defending the authenticity of the documents, and latterly insisting that whatever doubts about their documents, the underlying story about Mr Bush's poor National Guard attendance was true. CBS is to appoint an independent inquiry into its own behaviour. But the incident has further fuelled mistrust, not just of CBS and Dan Rather, its veteran anchorman, but of the media in general. The latter's credibility is vital, especially in the US presidential system where more of the political debate inevitably takes place through the media and press than is the case with parliamentary governments.