It's also possible that the DNC prioritized its research based on who was most likely to win the primary. Hillary has been the overwhelming favorite for a long time now, so I don't think it's all that surprising that most of their work has been undertaken with the assumption that she would be the nominee.

I bet they have similar files on Lincoln Chafee and Martin O'Malley, but it would have been foolish to invest as many resources in developing those as they did in the HRC file.

I saw some opposition research guys in the UVM Bailey Howe Library late last year. They stood out like a sore thumb, dressed like hipsters--in the special collections room, and pulling multiple boxes on Bernie Sanders at a time. I'd never really seen someone pull that much stuff at once before. Then again, I don't visit special collections that frequently.

One of the people who work at the library contrasted it with when Howard Dean was running for president. There were opposition research guys from that election. However, instead of dressing like hipsters, they wore black suits.

It's common for campaigns to run oppo on their own candidates.

If you can find something before an actual opponent does, you can pre-emptively deal with it.