It's after noon in Washington, but the jurors in the Scooter Libby trial haven't heard any testimony yet today. The trial was delayed initially today because Judge Reggie Walton had an appointment elsewhere, and for the last hour or so lawyers have been arguing over whether Patrick Fitzgerald can show the jury videotape of Scott McClellan denying, at a White House press briefing, that Libby had anything to do with the leak of Valerie Plame's identity.

Fitzgerald is going to win that argument; Walton is going to let him show at least abbreviated versions of the videotape. Why does it matter? Fitzgerald says McClellan's statements go right to the heart of his case, and here's how he lays it out:

Libby, angry that McClellan hadn't cleared him of involvement in the leak initially, took his complaints to Dick Cheney. And on Cheney's orders, McClellan did what Libby wanted: He told reporters that he'd talked to Libby, and that Libby had said that he wasn't involved. Once Libby had done that -- once he had arranged for the White House to put out the line that he hadn't been involved in leaking classified information -- Fitzgerald says that he was "locked in" to that story.

And that, Fitzgerald says, was Libby's motive for lying to the FBI and to the grand jury; he couldn't admit, after getting McClellan to say otherwise, that he leaked Plame's identity, so he chose to say that reporters told him about Plame instead.