Even most Americans probably gave up trying to follow the threads of the trial of I Lewis "Scooter" Libby long ago. So it is asking a lot to expect non-Americans to grasp the full significance of the former White House official's conviction on four counts of perjury and obstruction of justice yesterday. After all, the leak to the press of the name of a CIA agent who played a cameo role in the Iraqi weapons of mass destruction debacle in 2002 was itself a recondite enough affair. The role of Mr Libby, the vice-president's chief of staff, in efforts to frustrate a special prosecutor appointed to investigate the leak made an already complex story more labyrinthine still. The investigation was then diverted for many months into an introspective media debate about whether journalists should be required to testify about their conversations with Mr Libby. The eventual trial may have fascinated the Washington Beltway crowd, to whom Mr Libby, the former CIA analyst Valerie Plame, and her husband Ambassador Joseph Wilson are seasoned and familiar figures. But why should outsiders have to take it seriously too?

For two main reasons. The first concerns the ethics of the administration of which Mr Libby, as top aide to Dick Cheney, was such a senior member. George Bush came to the White House in January 2001 pledging to "change the atmosphere in Washington DC". By this he apparently meant two things: one, that he would govern in a dignified and rule-respecting way that supposedly contrasted with that of Bill Clinton; and, two, that he would try to end the intense partisan bitterness that had marked the Washington of the Clinton era. The Libby case is prosecution exhibit number one in support of the charge that Mr Bush never attempted to do any such thing. On the contrary. The Bush administration has been ruthlessly partisan, fuelled by enmities worthy of the Nixon era. The outing of Ms Plame was a criminal act against the wife of an administration critic. Mr Libby lied about it. He presumably did it to protect Mr Cheney, who wanted to punish the Wilsons. Mr Libby's conviction therefore raises very direct questions about Mr Cheney's own position.

The second reason is because, at bottom, Mr Libby's lies concerned Iraq. The administration wanted to invade Iraq. Mr Cheney, and through him Mr Libby, was not particular about how to do it. When Mr Wilson publicly questioned the weapons of mass destruction case for war he therefore made himself a Cheney enemy. As a consequence, the White House took its revenge on him through his wife. Mr Libby lied to protect not just his boss but his boss's unjust war. That's why yesterday's verdict matters. This affair is not over yet - not by a long chalk.