How about this tack:

They did nothing wrong and had no problem with the three independent investigations already completed. However, a fourth investigation appears to be a search for evidence in support a conclusion already reached. How much more bottom is there to get down to?

At this point several people have gone through the thousands of texts these two sent to one another and found nothing. Their performance on the job was not compromised, but they he was let go and she was already gone after the affair was made public. Be prepared for the GOP to seize on anything that can be stretched and manipulated into a narrative to support the witch hunt chant.

"The American people do deserve answers. Are you telling me that the first three investigations were done improperly and therefore we need a fourth? The American people deserve for their politicians to get things done right the first time or at least within the three strike rule, don't they? Otherwise, we as politicians seem inept or willfully running the cost up or heaven forbid, looking for something that doesn't exist. Which is it?"

** read this in a southern accent ** =)