Thursday's appearance by President Bush and Vice President Dick Cheney before the commission investigating the Sept. 11 attacks may provide commissioners a rare opportunity: the chance to piece together some of the most important information they have already gathered.
It's true the appearance is scheduled to be brief. Given their number and the time allotted, individual commissioners may be hardly able to get a word in edgeways. Neither the president nor vice president may be able to explain the actions, or lack thereof, of many layers of the US national security bureaucracy.
But only the nation's top officials can say what they thought the FBI was doing in the summer of 2001. Only they can solve important discrepancies in other officials' actions. Only Bush can answer one of the most burning questions of all - on Sept. 10, 2001, what sort of terrorist threat did he believe the nation faced?
"No one can speak to the president's state of mind other than himself," says Jim Walsh, an international security expert at Harvard's Kennedy School of Government.
The political controversy which has swirled around Thursday's interview has tended to obscure some of the substance it may provide. The White House agreed to the meeting only after considerable pressure was applied by the commission, and by Republicans who worried the president would otherwise appear obstructionist. The fact that Bush and Mr. Cheney will appear together has been fodder for conspiracy theorists and late-night comedians, whose general theme is that the vice president is there to do all the talking.
At a contentious White House briefing on Tuesday, reporters pressed spokesman Scott McClellan to say why the session would not be recorded. He denied that the point was to "put a little fuzziness in the proceedings," as one questioner charged.
The ground rules mimic those laid out for President Ronald Reagan when he appeared before a Congressional committee investigating the Iran-Contra affair, according to administration officials.
"It's extraordinary for a sitting president of the United States to sit down with a legislatively created commission," said Mr. McClellan. McClellan and other officials have said that they believe the point of the interview is to allow the commission to paint as complete a picture as possible of the events leading up to the 9/11 attacks. Commissioners have publicly agreed - but some have pointed out that this does not mean the questions will be easy.
Indeed, Bush is likely to be asked directly about his response to the increased flow of warnings in the summer of 2001 that Al Qaeda was planning to attack inside the US. Did he see those in his daily intelligence brief? What was his reaction?
Bush has said that he thought the FBI was going hard after possible terror cells in the US at that time. Yet testimony before the commission established that the FBI's estimate of ongoing terror investigations in 2001 was incomplete, or exaggerated. What numbers were provided to the Oval Office?
"What [commissioners] need to do is see what the president and vice president have to say about issues already raised," says Robert Pfaltzgraff, a security expert at Tufts University's Fletcher School.
The nation's top two elected officials may also be asked about important inconsistencies in testimony the officials have already taken.
National Security Adviser Condoleezza Rice, for instance, told commissioners that, in the summer of 2001, under her guidance, the administration was preparing a major strategy paper for dealing with Al Qaeda. She insisted that this strategy contained military options if diplomacy failed.
Deputy Secretary of State Richard Armitage, however, disagreed with this. He testified that there were no military options in this strategy document.
"I think that was amended after the horror of Sept. 11," he said publicly.
The now-famous August 6 Presidential Daily Brief from the CIA concerning possible Al Qaeda plans to attack within the US is also a likely subject. Did the president ask for it (as his staff contends), or did the CIA provide it on their own (as CIA officials contend)? And, what did the president think, or think about doing, after he saw it?
The president's actions on Sept. 11 itself may be scrutinized, as well. The commission is attempting to establish if US fighters might have been able to reach some of the hijacked airliners in time to shoot them down, for instance. Commissioners may press Bush on exactly when he gave the extraordinary order that the military could consider those planes as targets.
That's a lot to discuss in one morning, however - particularly if the interviewees provide lengthy answers, as Dr. Rice did during her appearance before the panel. Thus the commissioners do not face an easy job.
"They will have to encourage the president and vice president to answer quickly," says Harvard's Jim Walsh. "But they won't be able to intervene with them, as [they did] with past witnesses, out of respect for the office."