Mr. Libby’s prosecution became a symbol of the polarizing politics of the Iraq war during the Bush administration. Ms. Wilson’s husband, Joseph C. Wilson IV, was a former diplomat who wrote an op-ed article in The New York Times in 2003 implying that Mr. Cheney ignored evidence that argued against the conclusion that Iraq was actively seeking to build nuclear weapons.

To undercut Mr. Wilson’s criticism, administration officials told reporters that he had been sent on a fact-finding mission to Niger because his wife worked for the C.I.A., not at the behest of Mr. Cheney. But federal law bars the disclosure of the identities of C.I.A. officials in certain circumstances and the leak prompted a special prosecutor investigation.

Charged with lying to investigators about his interactions with journalists, Mr. Libby insisted he simply remembered events differently. But his version of events clashed with the testimony of eight other people, including fellow administration officials, and a jury convicted him. Mr. Bush decided that the prison sentence was “excessive,” but he said he would not substitute his judgment for that of the jury when it came to the question of Mr. Libby’s guilt.

Mr. Libby’s advocates argued that Patrick J. Fitzgerald, the special prosecutor, went too far because he had already discovered that the first administration official to disclose Ms. Wilson’s identity to a journalist was Richard Armitage, the deputy secretary of state in Mr. Bush’s first term, who was not charged. They also argued that Ms. Wilson was not undercover at the time and her employment was well known. Ms. Wilson has denied that she recommended her husband for the mission to Niger and said her career as a C.I.A. official was “over in an instant” once her identity was leaked.

The case tested the limits of journalistic independence. Judith Miller, then a reporter for The Times, went to prison for 85 days rather than disclose that Mr. Libby had discussed Ms. Wilson with her. She was freed after Mr. Libby released her from any promise of confidentiality.

The issue became a major point of contention between Mr. Bush and Mr. Cheney in the last days of the administration in late 2008 and early 2009. Mr. Cheney repeatedly pressed Mr. Bush to go beyond his commutation and issue a full pardon, bringing it up so often that the president grew irritated by the matter.

Mr. Bush assigned White House lawyers to examine the case, but they advised him the jury had ample reason to convict Mr. Libby and the president rebuffed Mr. Cheney’s request. Mr. Bush told aides that he suspected that Mr. Libby had thought he was protecting Mr. Cheney, the real target of the investigation.