Leading article: Questions of principle

The investigation itself has raised some awkward questions of principle. The most obvious is journalistic. Valerie Plame's name was made public two years ago by a small number of reporters who had all been briefed by "government sources". To identify a CIA officer, knowingly, is a federal offence, so Patrick Fitzgerald was appointed as special prosecutor to discover who was ultimately responsible. But to do so, he needed to have those journalists to testify before a grand jury as to who leaked this information.

It is a high principle of journalism that reporters do not betray their confidential sources. And Judith Miller of The New York Times, a journalist asked to testify, was willing to accept a four-month jail sentence rather than co-operate with the investigation. Yet these are exceptional circumstances. Ms Plame's name was not leaked in the interests of uncovering wrongdoing in government, but to discredit her husband, former ambassador Joseph Wilson, who had fallen foul of the Bush administration over Iraq. Do journalists owe a duty of confidentiality when they have been manipulated by their sources for political purposes?

In any case, others have been less resolute than Ms Miller and The New York Times. Time magazine gave the e-mails and notes of one if its reporters to the special prosecutor last week. These show that one source of the information on Ms Plame was almost certainly Mr Rove. This must be treated with the utmost seriousness. If it turns out Mr Rove knowingly made the identity of an intelligence official public, he has jeopardised US national security and ruined an individual's career. It is likely that his defence will be that he never actually named Ms Plame directly when briefing journalists - but rather that he mentioned that Mr Wilson's wife worked for the CIA and let the journalists work out the rest. But this is a mere technicality. Anyone who reads the notes submitted to the investigator can discern Mr Rove's intent. And it is not edifying. It is also worth noting that this information is emerging at a time when it is least damaging to the Bush administration. Had these documents come out a year ago, it could have derailed George Bush's re-election campaign.

Whatever steps the special prosecutor decides to take next, Mr Rove's proximity to the President must not protect him from the consequences of his actions.