Seemingly, even if we define David as a king against whom there is a rebellion, then if Absalom had won he would have been appointed a new king (as they say, “The king is dead, long live the king”) and would bring a male goat. He is no worse than all the kings of Israel who seized power in a revolution and became kings. (To think that there is some parallel system of “the real king” that continues unaffected reminds me of the idea that a rabbinic acquisition is ineffective on the Torah level, so that every object in the world has two layers forever and ever.)

Could you expand more on why there is room for that reasoning? Is there room to say that this is a special rule regarding the male goat, where he is not judged as a king, or that this is a special rule regarding rebellion, where he is judged as a king? Not just that he is generally allowed to kill, but that he is allowed to kill by virtue of the law of the king, as Maimonides writes. A practical difference would be, for example, whether he would be allowed to sit in the Temple courtyard like the kings of the House of David.

I don’t know anything about the laws of kings (I just once happened across this whole issue with Shimei by chance in some old pilpul), but my heart whispers to me that I once felt somewhere the idea that if a cause cancels something out, it cancels it only with respect to other matters, but not with respect to things of the same kind as the canceling cause itself, which continue to destroy. Though probably the heart is deceitful above all things and is whispering to me for nothing, something like déjà vu.

(That pilpul (Parashat Derakhim) said that Shimei son of Gera thought that just as he brings a she-goat, so too one can rebel against him and not be liable to death, and therefore he hurried to curse him and stone him. But Solomon, who contrived to have him killed in fulfillment of the instruction of his father David, thought in accordance with the law in Maimonides that with regard to rebellion he still had the status of king. I was only asking in order to understand, because seemingly Rabbi Shimei son of Gera’s reasoning sounds more compelling; so what did Rabbi Solomon son of David think, and what is the law we have in hand?)

I didn’t understand. You’re just repeating my reasoning.
This is not a special rule in one area or the other. Each law is judged on its own terms. It is obvious that a king can defend himself against a rebel even if temporarily his position is weaker, and along with that it is possible that he does not have the status of king without actual control (and it is also reasonable that Absalom does not yet have the status of king until he wins definitively).

It may be that the difference is between a nasi and a king.
The two titles usually coincide: “Who is a nasi? This is a king, as it is said: ‘from any of the commandments of the Lord his God’—one over whom there is none but the Lord his God.” But since he went into exile, the fear of others is upon him, so he is not a nasi; but he is still a king, and one who rebels against him rebels against the monarchy. And only a nasi brings a male goat.

Nice.

It should be noted regarding Lev’s comment that with regard to cursing a king too it says, “and you shall not curse a ruler among your people.”
As for the matter itself,
First, there is a dispute about this. Tamim’s question is only according to the opinion that he indeed obtained atonement like an ordinary individual.
Second, see Radbaz on Laws of Kings 3:8, Meiri Horayot 11a, and Abarbanel (on I Samuel in the matter of Nabal the Carmelite). What emerges from their words, according to my understanding,
is that a king is considered a king so long as he retains his kingship. (And therefore according to that opinion in the Jerusalem Talmud he obtains atonement like an ordinary individual.) However, one must distinguish between the kings of Judah and the kings of Israel. A king of Judah receives his authority through a prophet or through the consent of the community as a whole, whereas a king of Israel receives his power also through force of arms.
If so, in the kingdom of Judah Absalom certainly did not have the status of king, since he acted by force of arms. But since David was anointed by the prophet, even though he was not holding the kingdom in practice, one must still treat him with the honor due a king. And no one else could replace him except by consent.

Killing someone who curses a king is not a punishment for that prohibition. And maybe indeed when a king is fleeing, at the time when he obtains atonement with a she-goat, the prohibition of “you shall not curse” also no longer applies to him (but still, one who curses him may be put to death under the law of the king). As for Absalom—if he had won, there would have been plenty of public consent.

One can discuss public consent that comes by way of force of arms.
In any case, David’s honor as king at that time is not in doubt.

See the little book called II Samuel; there it says that the people’s consent was with Absalom afterward without any force of arms at all—except that after David won, all the people crawled back to him on all fours.

Shimei too came back and apologized after Absalom’s death. And one could say that while David was fleeing from Absalom he did not have the status of king, and therefore Shimei was not liable to death (and Maimonides mentioned him only as an example). Then, when David returned, Shimei came to ask forgiveness in order to make it known that now he was not cursing the king.

But this still remains puzzling: what does asking forgiveness help? He still thinks the same thing about David—that he is a man of blood—so what good does asking forgiveness do?

And perhaps for precisely this reason David and Solomon, and likewise Maimonides, held that Shimei was liable to death—not because David was king at the time Shimei cursed him, but because David was king afterward and the curse was still in force, except that for other reasons the matter was postponed.

And by the way, it seems from the stories in the book of Samuel that even if a king has the authority to kill a rebel against the monarchy, the rebel against the monarchy still has the right to defend himself, flee, and even kill the king’s men, somewhat as we saw with David and Saul and with David and Absalom.

A. Shimei. Why the puzzlement, and how is this different from any repentance? Shimei claimed that he recognized his mistake and knew that he had sinned. If you want to argue that obviously he was just a convert lion and lying—fine, but at least he tried to persuade with an argument that has some substance. Besides, the Sages explained, and there is support for it in the verses, that Shimei hinted to him that if David killed him, “the people” would not rejoice—“and behold, I have come today first of all the house of Joseph” (implying: if you do not accept me, then perhaps the rest of Joseph will also not come, as the Sages said). And therefore when David spared him he said, “Do I not know that today I am king over Israel?” My memory is already hazy here too; the homily in Parashat Derakhim deals with this whole issue.
B. According to your view, if someone cursed a king before he was appointed, would the king be allowed to kill him? That sounds very difficult.
C. David did not rebel against Saul, and therefore obviously he was allowed to defend himself (in the spirit of the halakhic interpretation of the Hebrew Bible in Parashat Derakhim). What exactly did you mean to bring from David and Absalom? I didn’t understand.

A. That’s what I was hinting at—that there were other reasons he wasn’t killed.
B. A difficulty. But one could distinguish between an ordinary curse directed at a person who is not a king, where there is no degradation of the monarchy even when he is later appointed king, and Shimei’s curse, which came to degrade David as king and to claim that he was unfit for kingship because of his “mafioso” character traits—a claim that still remained in force even after David returned and was reappointed king.
C. The Rabbi connected David’s ability to kill Shimei to the fact that he still retained some aspect of kingship, and therefore he could also fight Absalom. According to my explanation, that David had no status of king at all, the question arises: how could David fight Absalom, who seemingly was king? To that I answered that he fought not by virtue of kingship that remained in him, but by the reasoning of “if someone comes to kill you, rise early and kill him first,” even if that person is the king.

C. Ah, clever. But even if David was not king at the moment, he would still be allowed to reclaim the monarchy because it rightfully belongs to him, just as Jehu son of Nimshi was allowed to kill Jehoram by Elisha’s command even though Jehoram had not been plotting to kill Jehu.

And maybe David also thought that by showing mercy to Shimei he would prove that he was not a man of blood and would silence that accusation, which apparently was present among the people (Shimei was an elitist and gathered a thousand men; apparently he was not some fringe crank).

A. You’re missing an important proof that I pointed to yesterday by hint, and that is Nabal the Carmelite.
Nabal rebelled against David’s monarchy, but David was not yet king (because Saul was the king), so how then did David want to judge him as a rebel?
The answer is as Abarbanel wrote: since David had already been anointed by Samuel, he must be honored as king even though he had no control over the people. That is also the reason why he still had the status of a king who must be honored even while he was fleeing.
B. I doubt that Absalom is considered king according to the laws of kings. Because if so, there is indeed a reverse difficulty: how could David fight Absalom, king of Israel? Granted, in David’s case we could say, “if someone comes to kill you, rise early and kill him first,” but what shall we say about David’s men—King Joab, Abishai, Ittai the Gittite, and the entire army? (I’d be happy if you have a proof for the matter.)

C. Also, from David’s words to Abishai, who wanted to kill Shimei, it does not sound as though he exempted him from the law of a rebel (because now he is not king). Rather, he said to leave him alone because the Lord had told him to curse.
D. (A side note unrelated to the issue of “the king in flight.” Against the pilpul you cited from Mishneh LaMelekh, based on Yalkut Shimoni, that David had a reason for not killing Shimei: it is brought in the Talmud, Megillah 12b—Rava said: The community of Israel said to the other side, “See what the Judean did to me and what the Benjaminite repaid me. What did the Judean do to me? David did not kill Shimei, and from him Mordechai was born, provoking Haman’s jealousy against him. And what did the Benjaminite repay me? Saul did not kill Agag, and from him Haman was born, who oppressed Israel.” It sounds as though there is, so to speak, a claim against David in this matter…)