I happen to have a spreadsheet of all Reddit AMA backfires (https://docs.google.com/spreadsheets/d/1DTCRqeQvjOZAyngC31kn...), and the common thread among AMA disasters is the original poster being genuinely unaware that they might be received negatively (or they are just trolls). I don't think that will be the case with the WaPo, anyways.
AMADisasters was the reason I made the list. (it turns out the mods would not let me post it there because it would make finding AMADisasters too easy)
(For posterity, here's a spreadsheet of all Reddit thread backfires in general: https://docs.google.com/spreadsheets/d/1bUSN7-nocMJz2Wo1KTIn...)