According to settled law, the entire process of nomination, advise and consent, and appointment is discretionary on the part of all involved. There are no "duties," Constitutional or otherwise, extant. That understanding extends from Chief Justice Marshall in "Marbury v. Madison"  (1803) through the DOJ's Office of Legal Council opinion of 1999.

http://reformclub.blogspot.ie/2016/03/re-letter-to-boston-globes-letters.html