Why does the Torah sometimes use the expression "Vayechazek Libo", and other times "Vayachbed Es Libo"?
Rashbam (Pasuk 23) and Seforno (8:11): Pharaoh was a strong man who was capable of hardening his heart even when the odds were stacked against him. Even he however, had to assert himself to play it tough following the terrifying plagues of frogs and wild beasts. 1 Hence the Torah writes "Vayachbed Es Libo". 2