As I’ve read, Melson has gone on record that he won’t “take the fall” for Holder or Obama. Good that he won’t. And Melson has told Issa that “smoking gun” document(s) are being withheld from Congress.
That’s the way I understand it, but I think it’s possible that Issa has copies of something, given to him by Melson. Whether that includes the “smoking gun” or not, I don’t know. The video indicates Melson gave him something. Perhaps Issa feels compelled to make Holder hand it over, and maybe he needs it to come from Justice to bear more weight.