Oh no! That's very concerning and I hope you can find some good input!
Basenjis are notoriously "one person" dogs. Is he usually with someone else in the family (you?) - meaning, who do you believe he thinks is "his person"? I ask because while my basenji otherwise adored my husband, when I was distraught or unwell she would become defensive if he did anything she perceived as him trying to separate her from me.
Another thing to consider, if your daughter is old enough, was she menstruating? I know, it's an odd question. I don't have any experience with male basenjis but my parents had a male Boston Terrier that would get weirdly defensive when it was my "time". It looked like aggression though I thought perhaps it was more his screwy way of trying to herd/control my movements. It's a weird possibility but maybe something to consider if other things don't make sense.