While I have been ruminating on the following idea and its consequences for a number of years, particularly around Purim, a question over at Mi Yodeya about whether or not Amalek has been destroyed prompted me to present the idea in its basic form:
While I haven't seen it spelled out per say, presumably because the mitzvah still has a very real relevance, it seems clear from the sources that while it wasn't preformed in the "lechatchila"/optimal manner the mitzvah in its primary manifestation was fulfilled by Shaul (or more correctly Shmuel):
From the Gemara in Sanhedrin (20b, see also Rashi) we see the mitzvah of cutting off Amelek was a prerequisite for the building of the Temple:
סנהדרין כ:ב תניא רבי יוסי אומר שלש מצות נצטוו ישראל בכניסתן לארץ להעמיד להם מלך ולהכרית זרעו של עמלק ולבנות להם בית הבחירה ואיני יודע איזה מהן תחילה כשהוא אומר כי יד על כס יה מלחמה לה' בעמלק הוי אומר להעמיד להם מלך תחילה ואין כסא אלא מלך שנאמר וישב שלמה על כסא ה' למלך ועדיין איני יודע אם לבנות להם בית הבחירה תחלה או להכרית זרעו של עמלק תחילה כשהוא אומר והניח לכם מכל אויביכם וגו' והיה המקום אשר יבחר ה' וגו' הוי אומר להכרית זרעו של עמלק תחילה וכן בדוד הוא אומר ויהי כי ישב המלך דוד בביתו וה' הניח לו מסביב וכתיב ויאמר המלך אל נתן הנביא ראה נא אנכי יושב בבית ארזים וגו'“It has been taught: R. Jose said: Three commandments were given to Israel when they entered the land; [i] to appoint a king; [ii] to cut off the seed of Amalek; [iii] and to build themselves the chosen house and I do not know which of them has priority. But, when it is said: The hand upon the throne of the Lord, the Lord will have war with Amalek from generation to generation ,(Exodus 17:16) we must infer that they had first to set up a king, for ‘throne’ implies a king, as it is written, Then Solomon sat on the throne of the Lord as king (1 Chron. 29:23). Yet I still do not know which [of the other two] comes first, the building of the chosen Temple or the cutting off of the seed of Amalek. Hence when it is written, And when He giveth you rest from all your enemies round about etc., and then, Then it shall come to pass that the place which the Lord your God shall choose, (Deut. 12:10) it is to be inferred that the extermination of Amalek is first. And so it is written of David, And it came to pass when the king dwelt in his house, and the Lord had given him rest from his enemies round about, and the passage continues; that the king said unto Nathan the Prophet: See now, I dwell in a house of cedars etc. [Soncino]
Which is brought down as halachah in the Mishneh Torah:
משנה תורה: הלכות מלכים ומלחמותיהם א:ב מנוי מלך קדם למלחמת עמלק, שנאמר: "אתי שלח ה' למשחך למלך עתה לך והכיתה את עמלק". והכרתת זרע עמלק קודמת לבנין הבית, שנאמר: "ויהי כי ישב המלך בביתו וה' הניח לו מסביב מכל איביו. ויאמר אל נתן הנביא, אנכי יושב בבית ארזים וגו'"The appointment of a king should precede the war against Amalek. [This is evident from Samuel’s charge to King Saul] (I Samuel 15:1-3): “God sent me to anoint you as king . . . Now, go and smite Amalek.” Amalek’s seed should be annihilated before the construction of the Temple, as [II Samuel 7:1-2] states: “And it came to pass, when the king dwelled in his palace, and God gave him peace from all enemies who surrounded him, the king said to Nathan, the prophet: Look! I am dwelling in a house of cedar, . . . [but the ark of God dwells within curtains]. [Moznaim]
This seems consistent with the peshuto shel mikra (plain meaning) of 1 Samuel 15 where it is related that King Saul destroyed the nation of Amalek, only sparing King Agag and animals (although he was not supposed to spare either). King Agag, however, was executed by Shmuel after he rebuked Saul for his disobedience. That this commandment found its historical fulfillment doesn't detract from its status as a commandment. Yet it seems to me that although Amalek was destroyed in a literal sense, a prerequisite for building the Temple as we have seen, by failing to do so as commanded Saul allowed the ["disembodied"] spirit of Amalek to live on. It is in this sense that we find the primary significance of Haman's descent from Amalek regardless of how literal we should take the midrashim about Agag siring offspring during his brief period in custody. Haman is called Agagi, not Amalaki, he carries on the "spirit" and "mission" of Amalek not as Amalek strictly defined but because the Bnei Yisrael failed to preform the mitzvah as commanded even though the end result was equivalent.
