What are "ha'Badim"?
Rashi, Targum Yonasan: Its magicians. Rashi - this is like "Mefer Osos Badim" (Yeshayah 44:25). They are called so, for they are Bodim (concoct) and say lies.
Radak: They are liars. This is like "Badecha Mesim Yacharishu" (Iyov 11:3). They are the magicians.
Malbim: They are astrologers.
Brachos (63b): They are Chachamim who engage in Torah alone. (For this, they are worthy to be punished via the sword, and they become foolish.)
What is the meaning of "No'alu"?
Radak, Targum Yonasan: It is foolish. The same applies to "No'alu Sarei Tzo'an" (Yeshayah 19:13), "Asher No'alnu" (Bamidbar 12:11).
How did they become foolish?
Rashi: Via their magic. Radak - now that the evil came upon them, and they did not know anything, their magic did not help.
Malbim: They will not become wise 1 any more in astrology.
Refer to 50:36:1:4.
Surely they did not foresee the fall of Bavel. If not, they are not foolish! Malbim means that they will cease to study astrology, or people will cease to consider them wise. (PF)