Why did he compare them to a bereaved bear?
Radak: It is very bitter when its cubs are killed, and fights fiercely and bitterly against any man it finds then.
Malbim: One assumption of Achitofel's counsel is that David and his men are crushed and weak, and a sudden threat will make them fear greatly. This is wrong - they are Giborim, and if they are pursued, they will not retreat. They will risk their lives and fight!
Why did he say that David is an Ish Milchamah?
Rashi: He knows war strategy and ambush. He is sure that we will pursue tonight, so he will not lodge with the rest of his people. (Rather, he will hide in a hole - verse 9.)
Malbim: The second assumption of Achitofel's counsel is that David will lie [to sleep] among his troops, without fear. This is wrong. (Refer to 17:8:2:1.)
What is the meaning of "v'Lo Yalin Es ha'Am"?
Radak: This is like "Im ha'Am." He will hide in a hole (verse 9), and no one will know where he is. Therefore, Achitofel's counsel to kill only David will not succeed.
