Now someone told David: “Ahithophel is among the conspirators with Absalom.” So David pleaded, “O LORD, please turn the counsel of Ahithophel into foolishness!”
Nothing, it seems, appeared to David more threatening in Absalom's plot than that Ahithophel was in it; for one good head, in such a design, is worth a thousand good hands. Absalom was himself no politician, but he had got one entirely in his interest that was, and would be the more dangerous because he had been all along acquainted with David's counsels and affairs...
Commenting on 2 Samuel 15:31-37
And one told David,.... That came either from Hebron or from Jerusalem: Ahithophel is among the conspirators with Absalom; Absalom sent for him, and it seems he came to him, and continued with him, see Sa2 15:12, and David said, O Lord, I pray thee, turn the counsel of Ahithophel into foolishness; either suffer him to give foolish counsel, or confound the schemes projected by...
David said, Turn, O Lord, . . . the counsel of Ahithophel--this senator being the mainstay of the conspiracy.