1 Kings 1:7

Conferred with Joab. With the support of the commander in chief, Joab, Adonijah hoped to win over the army, and through the high priest, Abiathar, to secure also the support of the priesthood. Both Joab and Abiathar had been very close to David and had performed noble service for him in difficult and troublous times. Joab was a hard, bold, and at times unscrupulous man, imperious on occasion and even disobedient to the royal commands. Abiathar was the son of Ahimelech, who suffered death in David’s cause. Abiathar had been one of David’s firmest friends, having been with him in his wanderings when he fled from Saul (1 Sam. 22:20-23), serving him when he was king at Hebron (2 Sam. 15:35), and fleeing with him when Absalom rebelled (2 Sam. 15:24, 29, 35, 36; 17:15; 19:11). The reason for his defection at this time is not clear, but it might be that he did not view Adonijah’s conduct as an actual rebellion. David’s designation of Solomon for the throne might have been looked upon as springing from excessive fondness, and the assumption of the crown by the eldest son might have seemed only right and justifiable. On his part, Joab may have given support to Adonijah because of a grudge against the king for demoting him (2 Sam. 19:13).