> The fact that he slept with a subordinate shows bad judgment, but isn't a huge deal (although improper and opens up potential quid-pro-quo lawsuits)

That is absolutely a huge deal, I have no idea why you don't think it is. That is the kind of behavior which anyone in an American workplace knows is not tolerated in the slightest and would lead to firing. The fact that he did it anyway shows he has shockingly poor judgement.