>> reporter: bernie sanders was chairman during the height of the wait list scandal. but critics like the founder of the iraq veterans administration knew it. >> he was positioning it as a smaller issue than it was while veterans were dying waiting for care. >> reporter: he says he had to know what was going on where the house investigators were digging up records, swearing in whistleblowers. >> he was at the helm during the biggest scandal in v.a. history. the question for bernie sanders is where were you? why didn't you conduct more oversight? why didn't you get to the bottom of this and listen to the veterans groups who came forward and said this was a problem? >> republicans were so troubled by the lack of oversight, they sent this letter to sanders