Rashi: It is about Nebuchadnetzar, who will enter the Heichal to destroy it, and not one of his soldiers protested. David also composed Tehilim 53 about Titus [who destroyed Bayis Sheni].

Radak: Also this is about Galus.

Malbim: It is for a miracle that Hashem did for David, to save him from an enemy that afflicted Yisrael. It is repeated below (Tehilim 53) with some changes. When the miracle of Sancheriv (his colossal camp was wiped out) in the days of Chizkiyah, they saw that this Mizmor is good to say to thank for this miracle, and they fixed it with a small addition and attributed it to David, for he authored [the initial version].

Rashi: Nebuchadnetzar - he said "E'eleh Al Bamasei Av" (Yeshayah 14:14).

Radak: The king of the nations that Yisrael are in their hands. Since he harms Yisrael and presses them, he thinks that there is no Elokim, no Judge and law in the world to pay a man according to his deeds.

Malbim: It is the king who came [to afflict Yisrael]. He denied Hashem's existence, just like Sancheriv sent to blaspheme the living G-d.

Radak: He and his nation [were corrupt].

Malbim: His entire camp did evils and abominations. Not one did good, even good behavior of Chesed or mercy. When one is found among them, that it seems that he believes in Hashem and gives honor to Him (like Chazal say that Nebuchadnetzar was in Sancheriv's camp, and he showed honor to Hashem ¹ . Therefore, he and 10 others survived - Sanhedrin 95b.) These do not have that merit.

Rashi: They are [his] deeds.

Radak: All corrupted their deeds. All their deeds are for evil, for they think that Hashem does not see.