R. Joseph B. Soloveitchik (Kol Dodi Dofek, ch. 10) famously quoted his father, R. Moshe Soloveichik, as explaining the following discrepancy in the Rambam's Mishneh Torah. In Hilkhos Melakhim (5:4) the Rambam writes that we cannot currently fulfill the commandment to destroy the seven Canaanite nations because "their memory has already been erased", i.e. they have been mixed in with other nations and we cannot identify them. However, regarding the commandment to destroy Amalek (ibid. 5:5), the Rambam does not write that their memory has been erased. Why not? R. Moshe Soloveitchik explained that this commandment applies to any nation that acts like Amalek, i.e. tries to destroy the entire Jewish nation. [R. Joseph Soloveitchik proceeded to apply this category to the Nazis.]
Was this explanation meant literally and halakhically, or was it a homiletical tool to make an important point?
R. Nachum Rabinovitch (Melumedei Milchamah, ch. 3) argues the latter. He points out that in Moreh Nevuchim (3:50) the Rambam explicitly writes that the decree was against zera Amalek bilvad, only the descendents of Amalek. And in Sefer Ha-Mitzvos (positive commandment 187), the Rambam writes that just like the commandment to destroy the seven nations does not apply in every generation since they have been spread among the other nations and are unrecognizable, so too the commandment to destroy Amalek. Therefore, writes R. Rabinovitch, clearly the idea of "their memory has already been erased" also applies to Amalek and there is no halakhic concept of a "spiritual Amalek". Then why doesn't the Rambam write that Amalek's memory has already been erased? R. Rabinovitch explains that this is precisely what is implied when the Rambam begins discussion of this commandment with "and also" (ve-chen). The same clause that was stated about the seven Canaanite nations also applies to Amalek.
However, it is possible that a careful reading of R. Soloveitchik's words can answer these questions. I quote now from the Gordon translation, n. 23 (pp. 113-114):
I heard the answer from my father of blessed memory. Every nation that conspires to destroy the Jewish people is considered by the halakhah to be Amalek. My father added that as concerns Amalek itslef we were commanded to perform two mitzvot: (a) [for the individual] to blot out the memory of Amalek , which is incumbent on everyone [to slay] any individual member of Amalek [that he encounters], as expounded in the Torah portion of Ki Tetzeh, "You shall blot out the memory of Amalek" (Deuteronomy 25:19), and (b) [for the community] to engage in communal military preparednes for war against Amalek, as it is explained in the Torah portion of B'shalach, "The Lord will wage war with Amalek from generation to generation" (Exodus 17:16). With relation to any other nation that stands ready to destroy us, we are [now after the time of Sennacherib] commanded to wage war against it [even] whil it prepares for war against us, and our war against it is a "War of Mitzvah", in accordance with the command of the Torah that "The Lord will wage war with Amalek from generation to generation." However, the destruction of individuals, which is derived from the Torah portion of Ki Tetzeh, refers only to the biological descendants of Amalek. The words of Maimonides include the obligation to wipe out individuals, which does not apply to any other antion that plots destruction against the People of Israel. However, since the obligation of warring with Amalek pertains to such a nation (as well), he did not employ the phrase "And its memory has already been lost."In other words, there are two aspects (dinim) to this commandment:
- Wiping out Amalek's memory: This is learned from Deut. 25 and is an obligation on individuals. It only applies to descendents of Amalek, and therefore does not currently apply because "their memory has been already been erased."
- Warring with Amalek: This is learned from Ex. 17 and is on the community. It applies even to a nation that acts like Amalek.