As I said earlier: I think the Dems will try the 'Estrada' gambit in that Roberts also worked in the solicitor general's office. They demanded Estrada's private notes, remember?
Yes - and they did not demand Roberts' papers when he was confirmed to the same court that Estrada was nominated for. Their motivations in that case against Estrada were obviously racist because of that - as McConnell and Hatch point out at the time during floor debate on Estrada's nomination.
However, now that you mention it, they will use that old card since he is now nominated to the SCOTUS.
I've heard the Democrats will be demanding his private notes from 20 years ago.