They would have argued line-by-line that he jeopardized national security and put agents' lives in danger by revealing sources and methods.
I think Barr having declas power allows Huber to get anything he needs, and if anything goes public, POTUS will be insulated from the impeach because he just gave Barr power. This would only matter in the first term - cant get impeached and jeopardize not being electable for necessary second term. But in second term they'd never have time to remove him from office if he chooses to do it himself.
Probably a bunch of snake Republicans would have joined Dems in impeaching for the declas.