What is the meaning of "Maskil Tzadik v'Veis Rasha"?
Rashi: Hashem, the Tzadik of the world, puts His heart to cut off the Rasha's house, e.g. the memory of Amalek.
R. Yonah: Many think that a Tzadik does not understand a Rasha's Midos, excuses and natures, for they are the opposite of a Tzadik's nature. This is wrong. A Tzadik contemplates a Rasha's ways of guile and his intents, and understands them. Chazal said 'lest swindlers say that Chachamim do not understand our deeds' (Bava Basra 89b).
Malbim: Also when a Rasha's house is serene - Beis Rasha hints to this - the Tzadik understands the reason (refer to 21:12:2:2).
What is the significance of "Mesalef Rasha la'Ra"?
R. Yonah: Because a Tzadik understands a Rasha's intent and nature, he tilts and judges him to be guilty in his deeds and words. One should judge a person favorably only if most of his deeds and the root of his intent is on the good path.
Malbim: A Rasha's serenity causes him to increase evil. If Hashem would punish him immediately, he would fear to do evil. Also, his serenity hastens his punishment - "u'Meshalem l'Son'av El Panav Leha'avido" (Devarim 7:10). This causes evil [to him], according to most of the reasons given for a Rasha's success. It is in order to hastens his evil and pay his punishment.