The case has its connections to Mr. Trump because Mr. Fitzgerald was friends with James B. Comey, who was then the deputy attorney general who assigned him the investigation after the attorney general recused himself. Mr. Cheney long suspected that Mr. Comey was taking revenge for a dispute between them over the legality of a surveillance program.
Mr. Comey would go on to become the director of the F.B.I. who was fired by Mr. Trump last year in the midst of the Russia investigation. His dismissal led the deputy attorney general, Rod J. Rosenstein, who was in charge after the recusal of Attorney General Jeff Sessions, to appoint Robert S. Mueller III as special counsel to take over the inquiry.
https://www.nytimes.com/2018/04/12/us/politics/trump-pardon-scooter-libby.html
So this is all vendetta stuff. Hopefully it’s part of a larger deal Trump is making by helping out Cheney.