It seems that Senator McCaskill's family has a Labor Day weekend pig roast tradition and she Tweeted a photo of her Son in Law carving the hog for the meal. Wowser did that tweet and photo cause a firestorm of disapproval by many. Other responses were supportive and funny, but most were very unhappy with her and what was seen as animal cruelty.
Here's the photo and her tweet: "Son-in-law in his trash bag apron carving pig #2 in new Labor Day weekend family tradition."
Many replies to this tweet wondered about him wearing a trash bag. Here is the link to read the pig roast kurfuffle.