Or HaChaim on Exodus 5:2/אור החיים על שמות ה׳:ב׳

1 אשר אשמע בקולו, "that I should listen to His voice." Pharaoh challenged Moses regarding his G'd's great power. Surely the Jewish G'd was not so powerful that He could demand such obedience in a matter of such overriding importance! He added gratuitously: "to dismiss the Jewish people," meaning that however great His power it would surely not suffice to liberate the Jewish people. Pharaoh did not mean to concede that he did know of the Jewish G'd after all, but that the latter was not great enough to make such a demand; rather he said: 1) "I do not know of Him;" 2) even if I would be told that He does indeed exist this would not mean that He could demand the freeing of the Jewish people." The word גם refers to a hypothetical situation.