1)
What is the meaning of "va'Yakehu Kaval Am"?
1.
Rashi citing Targum Yonasan: He struck him in front of the nation. Radak - "Kaval Am" is two words, like 'Neged ha'Am.'
2)
The Yerushalmi (Horiyos 3:2) says that Melech Yisrael and Melech Yehudah both had the law of Nasi (for Korban Chatas until [Zecharyah, the fourth generation from] Yehu. After this, murderers seized power. Also before this, Basha, Zimri and Amri seized power via killing Nadav, Elah and Zimri, respectively, without a Navi's mandate!
1.
Torah ha'Temimah (12): Nasi is only if the nation accepts him. After Zecharyah, the one who killed the 'king' seized power without the nation's consent.