The latest incident began with a sequence of questions for President Bush at his January 26 press conference. First, he was asked whether he approved of his administration's payments to conservative commentators. Government contracts had been granted to three pundits, who had tried to keep the funding secret. "There needs to be a nice, independent relationship between the White House and the press," said the president as he called swiftly on his next questioner.

Jeff Gannon, Washington bureau chief of Talon News, rose from his chair to attack Democrats in the Congress. "How are you going to work - you said you're going to reach out to these people - how are you going to work with people who seem to have divorced themselves from reality?"

For almost two years, in the daily White House press briefings Gannon had been called upon by press secretary Scott McClellan to break up difficult questioning from the rest of the press. On Fox News, one host hailed him as "a terrific Washington bureau chief and White House correspondent". Gannon was frequently quoted and highlighted as an expert guest on rightwing radio shows. But who was Gannon? His strange non-question to the president inspired inquiry. Talon News is a wholly-owned subsidiary of a group of Texas Republicans. Gannon's most notable article had asserted that John Kerry "might some day be known as 'the first gay President'".

Gannon also got himself entangled in the investigation into the criminal disclosure of the identity of covert CIA operative Valerie Plame. Plame is the wife of former ambassador Joseph Wilson, who was sent by the Bush administration to discover whether Saddam Hussein was procuring uranium in Niger for nuclear weapons. He learned that the suspicion was bogus; appalled that the administration lied about nuclear WMD to justify the Iraq war, he wrote an article in the New York Times about his role after the war.

In retaliation, Plame's CIA cover was blown by administration officials. Gannon had called up Wilson to ask him about a secret CIA memo supposedly proving that his wife had sent him on the original mission to Niger, prompting the special prosecutor in the case to question Gannon about his "sources".

His real name, it turned out, is James Dale Guckert. He has no journalistic background whatsoever. His application for a press credential to cover the Congress was rejected. But at the White House the press office arranged for him to be given a new pass every single day, a deliberate evasion of the regular credentialing that requires an FBI security check. It was soon revealed. "Gannon" owned and advertised his services as a gay escort on more than half a dozen websites with names like Militarystud.com, MaleCorps.com, WorkingBoys.net and MeetLocalMen.com, which featured dozens of photographs of "Gannon" in dramatic naked poses. One of the sites was still active this week.

Thus a phony journalist, planted by a Republican organisation, used by the White House press secretary to interrupt questions from the press corps, protected from FBI vetting by the press office, disseminating smears about its critics and opponents, some of them gay-baiting, was unmasked not only as a hireling and fraud but as a gay prostitute, with enormous potential for blackmail.

The Bush White House is the most opaque - allowing the least access for reporters - in living memory. Every news organisation has been intimidated, and reporters who have done stories the administration finds discomfiting have received threats about their careers. The administration has its own quasi-official state TV network in Fox News; hundreds of rightwing radio shows, conservative newspapers and journals and internet sites coordinate with the Republican apparatus.

Inserting an agent directly into the White House press corps was a daring operation. Until his exposure, he proved useful for the White House. But the longer-term implication is the Republican effort to sideline an independent press and undermine its legitimacy. "Spin" seems quaint. "In this day and age," said press secretary McClellan, waxing philosophical about the Gannon affair, "when you have a changing media, it's not an easy issue to decide or try to pick and choose who is a journalist." It is not that the White House press secretary cannot distinguish who is or is not a journalist; it is that there are no journalists, just the gaming of the system for the concentration of power.

· Sidney Blumenthal is former senior adviser to President Clinton and author of The Clinton Wars

sidney_blumenthal@yahoo.com