Abraham is nearly the thickest man in history. Or the weakest. After prostituting his wife, then Sarai, to the pharaoh of Egypt he profited his purse greatly though you could reasonably argue that Lot’s misfortune was a direct result of Abraham’s sin. But here he is again willing to sell his wife for some security.
I was angry just reading that. Abimelech was apparently angry about this as well.
This exchange is so telling:

Abimelech went on to Abraham, “Whatever were you thinking of when you did this thing?”

Abraham said, “I just assumed that there was no fear of God in this place and that they’d kill me to get my wife. Besides, the truth is that she is my half sister; she’s my father’s daughter but not my mother’s. When God sent me out as a wanderer from my father’s home, I told her, ‘Do me a favor; wherever we go, tell people that I’m your brother.’”

Abraham answers the question very simply, but I’m not sure he really answered Abimelech at all. In fact, I wonder if this is really a rhetorical question, because there’s really no satisfactory answer.

Abimelech’s servants were shocked, and I continue to be confounded by Abraham.