The first couple of days that Bernie was here, Kirby wanted to eat him
I wasn't too worked up about, because I expected this from him. Basically, I monitored every interaction for the first 48 hours. Now, (3 mos later) I can't say they are best friends (Bernie's best friend is Ginger) but thats more because of the 14 year age difference. But they do get along and there are no more battles. Not even over food.
I guess just hang in there. Allow for adjustment time. Some growling and posturing are okay until they decide who is boss...Just limit their interactions, spend more one on one time with the original dog (not the new one) etc., and give it some time.
Bless you for rescuing.