Atticus is not plotting and scheming, he is not a person, he is a dog. He is topdog and as such it sounds to me as if he's probably just displaying typical top dog traits. If he is topdog then you-as much as it might annoy or upset you- must reinforce his position. Feed him first, pet him first, give him the most attention, don't get involved in snaps or snarls unless there is serious threat of violence and in a few days they will have sorted their pecking order out and will be best friends again. I've seen this loads of times in a pack and the worst thing a person can do is attribute human reasoning to a dog or dogs. Leave then settle their places and I'm fairly certain in a few days they will be back to their original group dynamic.