So we just got a new dog last week. My friend was getting evicted and I agreed to take in her chihuahua, he got fixed a few days ago and was fine that day because of the drugs lol. But the next day he put his paws on my husbands leg to get pet so my husband started petting him, and then my husbands dog got up and wanted to get pet too...he growled, husbands dog growled back then he snapped and it was a full on fight. We separated them for about 30 minutes and put him back in with the dogs. Since then he has gone after my husbands dog two times for no reason. Is this normal for a new dog? What can we do to stop this behavior?

*side note for further clarification we have 4 dogs and he is just going after my husbands dog