There is speculation that the House Oversight Committee might be pre-empting the OIG report in some way because they know the GOP establishment (McCain, Romney) could be implicated in criminal behavior.
House oversight has in past deployed various shenanigans to slow down or obstruct (such as with the IRS scandal). I'm not so trusting of Gowdy at this point and he might be comp'd too.
Nevertheless though the scandal seems so large/public that oversight could not do much to keep the cat in the bag with OIG.
https:// theconservativetreehouse.com/2018/04/16/trey-gowdy-requests-ig-horowitz-appearance-before-house-oversight-committee-may-8th-2018/