Sidney Blumenthal, 49, a former journalist for among others The New Yorker magazine, is the man behind the attendance of the Clintons and Tony Blair at today's New York University forum on "Civil society and the future of democracy".
Mr Blumenthal, a long-time friend of the Clintons, has strongly denied the suggestion that he was the source of adultery allegations against Representative Henry Hyde,chairman of the House Judiciary Committee, which considered whether to release the videotape of Mr Clinton's grand jury testimony, and will also decide on the institution of impeachment hearings.
The allegations, which appeared in a pro-Clinton Internet magazine, Salon, were denounced by members of Congress as a heinous slur against Mr Hyde. They noted also that Mr Hyde was the fourth member of Congress to find his past private life under a hostile microscope and pointed the finger in the direction of the White House.
Eight leading Republicans, including the House Speaker, Newt Gingrich, initialled a letter to the FBI, requesting an inquiry and naming Mr Blumenthal as a possible source on the basis of information from named television journalists that he had been tipping off selected media outlets.
If there is proof that Mr Blumenthal had anything to do with any of the recent slurs , his White House career would appear to be over. One source yesterday gave him until the end of the week.
Such a development would be embarrassing for the Blair camp, which has relied on him as its chief go-between with the Clinton White House. His loss could also leave British diplomacy in uncertain waters if the President is forced from office.