And the magicians did so— Here, as before, the grand test of their power would have been to have removed this plague of frogs from the land. But this was beyond the reach of their ability; see the following verses. See also Bochart's Hieroz. part 2: lib. 5 cap. 2 where there is an acute discussion of this miracle.
Related Commentaries of Exodus 8:7
Exodus 8:7
7 And the magicians did so with their enchantments, and brought up frogs upon the land of Egypt.