Tim Russert dodged a bullet today thanks to US District Judge Reggie Walton. If not for Walton, Russert could have been the biggest loser in the trial of I. Lewis "Scooter" Libby on charges that he lied to a grand jury about his role in leaking the name of a CIA operative.

Libby’s lawyers spent the better part of yesterday and this morning going after the NBC bureau chief, who is central to the case. Libby told grand jurors in 2004 he learned that Valerie Plame was a CIA agent from Russert; last week Russert testified in court that he never discussed Plame with Libby.

After Libby’s lawyers pummeled Russert in absentia this morning—he was in Boston—Judge Walton said, "This does touch upon his general credibility. If not the most important witness in this case, he’s one of the most important."

Libby lawyer Theodore V. Wells Jr. said, "He is the most critical witness in the case." Wells argued that Walton should force Russert to return to the courtroom and face more questioning.

Wells and Libby’s other attorneys argued that government’s deferential treatment of Russert in its investigation made him a less than credible witness. They also argued that Russert had portrayed himself as a paragon of journalistic fortitude because he said he had never revealed a source, when in fact he had done so in a conversation with an FBI agent.

"We were shocked," Wells told Judge Walton this morning, when we learned that Russert had been interviewed by an FBI agent about his conversations with Libby. Then Russert "went around the country" and passed himself off as reporter who protects his sources, Wells said.

Wells also challenged Russert’s claim under cross examination last week that he did not know that people testify before grand juries without their lawyers present. The matter was relevant because the government allowed Russert to give his testimony in his office, with his lawyer by his side.

Wells showed three video clips of Russert explaining on TV during the Clinton-Lewinsky scandal that if Clinton were called before a grand jury he would have to do so without his lawyer.

Wells presumably figured if he could get Russert back on the stand, he could catch him in a lie: How could Russert, a lawyer, say he didn’t know that witnesses appeared before grand juries without legal representation when he had explained the matter so well talking about Clinton?

If Wells could make jurors question Russert’s word, he could put a hole in the government’s case that Libby lied about his conversation with Russert—maybe make them think Russert was the liar.

Wells also wanted to show Russert as a witness beholden to the government for being allowed to give his testimony in his office. And he argued that the government buried Russert’s interview with the FBI agent in a footnote, thus allowing Russert to claim he had never revealed a source.

"Russert did talk to the FBI," Wells said. The fact that that the government did not reveal that conversation "goes to the heart of witness bias toward the government."

Special Counsel Patrick J. Fitzgerald said Wells’s arguments were "a stretch beyond a stretch." He added, "Mr. Russert endured a five-hour cross examination." Libby's lawyers "don't get to do a do-over."

By the end of Wednesday morning’s session, it appeared that Russert was going to get hauled back to court. If Wells's assertions did "touch upon Russert’s general credibility," as Walton said, he likely would bring Russert back.

And even if Russert came out of the questioning with his credibility intact, Wells probably would have drawn some blood along the way.

Judge Walton took the bench after the lunch recess and ruled against Libby’s side. He said Russert's testimony that he didn’t know that grand jury witnesses don’t have lawyers with them was "not central" to the case. Russert would not have to return to the witness chair, he said.

Like the entire proceeding, the Russert side show was many steps removed from the original offense, committed in 2003 when someone outed CIA operative Valerie Plame, which could be a violation of federal law.

Libby is not being tried for the leak. He’s being tried for lying during the investigation of the leak. And Wells wanted to damage the government’s case against Libby by bringing Russert's motives and credibility into question based on 9-year-old tapes and a footnote in a legal document.

Judge Walton wasn’t buying.