Kate Andersen Brower is a CNN contributor and the author of the forthcoming book "First in Line: Presidents, Vice Presidents and the Pursuit of Power." She has written two other books about the White House, "First Women: The Grace and Power of America's Modern First Ladies" and "The Residence: Inside the Private World of the White House." Unless otherwise noted, facts in this piece reflect research from those works. The opinions expressed here are hers.

(CNN) "I don't know Mr. Libby," President Donald Trump said when announcing the pardon of former Vice President Dick Cheney's chief of staff. "But for years I have heard that he has been treated unfairly. Hopefully, this full pardon will help rectify a very sad portion of his life."

However, since his 2007 felony conviction -- and his commuted 30-month prison sentence -- I. Lewis "Scooter" Libby has regained his right to vote and his license to practice law. Trump's decision, therefore, raises the critical question: Why is he granting a pardon for Libby at all?

Kate Brower

Libby spent years overseeing a mini fiefdom in the West Wing. He had an unprecedented triple title: Cheney's chief of staff and national security adviser as well as assistant to the President. In 2007, he was found guilty of lying about his role in the leak of undercover CIA operative Valerie Plame's name to the press and was convicted of perjury and obstruction of justice. Though George W. Bush commuted the sentence, Cheney insisted then that Libby should have been granted a full presidential pardon.

When I interviewed Cheney a month after Trump won the presidential election, it surprised me that eight years after leaving the White House he was just as angry about Bush's refusal to pardon his longtime right-hand man as he was the day he left the White House.

It was the most passionate he became in our more-than-hourlong discussion about the vice presidency for my next book. I asked Cheney if he would be pushing for a pardon for Libby (in the weeks between the election and our conversation, he said he had talked with incoming Vice President Mike Pence several times) but he would not answer the question directly.

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