Halakhah for Sanhedrin 40:19

And [also] that which they, may their memory be blessed, said (Sanhedrin 19b), "'Surely place upon yourself a king' - that his fear should be upon you"; meaning to say that we fear him, trust his words in every matter that he does not command against the commandments of the Torah and that we honor him with the full honor that can be fitting for flesh and blood. And in the hand of the king is the right to kill anyone who transgresses the commandment of the king who is established according to the Torah, or rebels against any matter [pertaining to him]. And there is no angle of iniquity in this, to the point where they, may their memory be blessed, said (Shabbat 56a) that Uriah became liable for his soul (life), when he said in front of David, "my master, Yoav" (II Samuel 11:11) - as he should not have mentioned mastery about any other man in front of the king. And [also] that which they, may their memory be blessed, said (Sanhedrin 20b) that in the hand of the king is the power to make a road in the middle of fields and vineyards, and that he may judge people according to what appears to him to be the truth - and even without clear witnesses. And [also] that which they said (Sanhedrin 22a) that we do not ride on his horse; we do not sit on his throne; we do not marry his widow; we do not use his scepter, his crown nor any vessels he uses. And all of this is for his stature and his honor. And when he dies, his vessels are burned in front of his bier. And [also] that which they said (Sanhedrin 19b) that [if] a king forgoes his honor, his honor is not foregone. And all of these things, they are all for the good of the people and for their benefit. And the laws of the king are all like they are explained in the book of I Samuel 8:11-17. [These] and the rest of the details of the commandment are elucidated in the second chapter of Sanhedrin, in the first chapter of Keritot and in the seventh chapter of Sotah. And this is from the commandments that are incumbent upon all of the community; [that is] upon the males, as it is proper for them to do these matters.

And this is from the commandments that are incumbent upon the entire community; and like the matter that they, may their memory be blessed, said (Sanhedrin 20b), "Three commandments were commanded to Israel at the time of their entrance to the land: to appoint themselves a king; to build themselves the Choice House (the Temple); and to cut off the seed of Amalek." And in truth is it that the obligation to kill them and destroy them from the world is also incumbent upon every male individual from Israel - if they have the power in their hands - in every place and at all times, if he finds one from all of their seed. And one who transgresses this and one from the seed of Amalek [chances upon] him - and he has the wherewithal in his hand to kill him - and he does not kill him, he has violated this positive commandment.