Did he not know Mordechai's nation until now?
Vilna Gaon: They told him that he does not bow because he is a Yehudi.
What is the meaning of "Lehashmid"?
Vilna Gaon: To eradicate their creed.
Haman was angry at Mordechai. Why did he want to destroy all the Yehudim?
Torah Temimah citing Megilah 13b: First (he wanted to kill) Mordechai alone; later, the nation of Mordechai, i.e. Chachamim; in the end, all the Jews.
Vilna Gaon: It would be disgraceful for him to kill only Mordechai, and also because he did not bow to him 1 . Also to kill only those in Shushan would be disgraceful.
Malbim: It was due to his evil and pride. Even though he saw that Mordechai's refusal is not due to his creed, rather, due to hatred (refer to 3:4:2:2), since they told him that his refusal is due to his creed, he hated all of Yisrael and their creed, and wanted to eradicate all who guard it.
This would show that he acts among adamancy about his honor. (PF)
Why is "Am Mordechai" repeated?
Vilna Gaon: It is because they are Am Mordechai, i.e. Yehudim; due to this, he did not bow.