Why didn't the Libby Defense call Libby and Cheney?

In the opening statements of the Libby Trial, Libby’s lawyer made a big point that Libby was being presented as the “fall guy” in order to protect Karl Rove. But it was never mentioned during the trial itself. Then throughout the trial, the Defense appeared ready to call Cheney and to have Libby testify in his own defense. Then, almost abruptly, the Defense rested without calling either, even though it is extremely difficult for someone on trial for lies and perjury to convince a jury of his innocence if he doesn’t testify himself. Without those Defense elements, what was presented was extremely weak. Sidney Blumenthal at Salon [Day Pass or membership required] explains what happened.

”[W]hy was Libby virtually passive? If Libby knew he was going to offer the barest defense, why didn't he do as Rove did, amending his grand jury testimony to reflect the truth? Why didn't Libby do as former White House press secretary Ari Fleischer did, turning state's evidence and being granted immunity in exchange for his testimony? What stopped Libby from risking indictment? What prevented him from making more than a minimal defense that invited conviction?
Libby could not plead the Fifth Amendment against self-incrimination. Had he done so he would not have been able to continue in his position as Cheney's chief of staff; he would have been compelled to resign. But why didn't he testify? Why didn't he make the case of Rove's perfidy that his lawyer suggested?

Libby and Rove's falsehoods in front of the grand jury, in which they blamed reporters for telling them about Plame, were a cleverly contrived coverup. They did not believe that the prosecutor would be able to break through the curtain of the First Amendment or untangle the tale as told by journalists. Both Libby and Rove relied on the same alibi, hiding behind the press corps that they had manipulated for years and whose erratic habits they knew well. But prosecutor Patrick Fitzgerald was not about to be confounded by this device. He knew the law was on his side, and he received a judicial decision forcing the reporters to testify.

Just as Fitzgerald was about to indict Rove for perjury and obstruction of justice, Rove got a lucky break. A reporter for Time magazine, Viveca Novak, a colleague of Cooper's and privy to his conversation with Rove, became consumed with an overwhelming desire to be an important inside dopester, and she rushed to inform Rove's lawyer, Robert Luskin, about Cooper's information. Suddenly, Rove produced an e-mail from Cooper that he had not produced to the prosecutor for a year, refreshed his memory, altered his testimony, and was off the hook. (Novak did not tell her editors or Cooper of her freelancing, and she was forced to resign, in effect sacrificing her career to save Rove by the skin of his teeth.) Libby was left to take the fall alone.[Snip]

Did something change in the defense after its opening statement about Rove (Libby "will not be sacrificed so Karl Rove can be protected") that led to its refusal to follow up during the trial? Did the prosecutor have new information that has not yet been made public about Libby and Cheney? If so, that evidence would have been irrelevant to the precise charges against Libby but might have come into play if Libby and Cheney testified. Their appearances might have made them vulnerable to additional perjury and obstruction charges if they were found to have lied on the stand. But who might have proved that?

The missing piece in the extensive evidence and testimony that detailed the administration's concerted attack on Wilson, orchestrated by Cheney, is the conversations among Libby, Cheney -- and Rove. Rove had made a deal with Fitzgerald. Rove changed his testimony, escaped prosecution and went back for a fifth time before the grand jury. Fitzgerald owned Rove.

Only if Libby and Cheney appeared could Fitzgerald cross-examine them about their discussions with Rove, which presumably Rove had already testified about before the grand jury. Rove was the hostile witness against Cheney whom the prosecution had waiting in the wings, the witness who was never called. If Libby had come to the stand in his own defense, and summoned Cheney as well, Fitzgerald might have been prompted to call Rove from the deep to impeach Libby's and Cheney's credibility and reveal new incriminating information about them. Instead, Libby remained silent, Cheney flew off to Afghanistan and Rove never appeared. Rove was the missing witness for the prosecution.

Assuming all this is correct, then it seems to me that Rove will be the key witness in an impeachment and trial of Dick Cheney. Fitzgerald seemed to make a point in his final statement that while he intended no more indictments, his evidence was available to the Congress.