שמואל ב, פרק ט״ו, פסוק ל״א

The alliance between a reckless, charismatic rebel like Absalom and a calculated, brilliant advisor like Ahithophel created a terrifying strategic threat. This formidable partnership sparked deep anxiety and prompted an immediate, desperate plea for divine intervention [ביאור שטיינזלץ].

The primary approach among commentators is that David was informed by a messenger that Ahithophel had joined the group of rebels [רש״י, רד״ק, מצודת דוד, ביאור שטיינזלץ, מצודת ציון]. Conversely, another perspective suggests David realized this on his own. Noticing his trusted advisor was missing, David deduced that Ahithophel had defected to the rebellion and personally broke the difficult news to his men [מלבי״ם]. By sharing this information, David hoped to provoke a response, looking for someone among his ranks clever enough to devise a counter-strategy against Ahithophel's legendary counsel. When it became clear that no one was capable of outsmarting the former advisor, David turned directly to God in prayer [אלשיך].

He pleaded with God to ruin Ahithophel's advice and reduce it to absolute foolishness [רש״י, מצודת ציון]. Commentators explain that this divine intervention could manifest in one of two ways. God could either strip Ahithophel of his wisdom, causing him to offer genuinely foolish advice, or He could alter Absalom's perception, leading the rebel leader to mistakenly believe that Ahithophel's brilliant strategy was actually deeply flawed [מצודת דוד, חומת אנך]. Ultimately, God answered this desperate prayer by sending Hushai the Archite into David's path. Through Hushai, an alternative plan was presented, and Absalom was led to accept his counsel instead of the advice of Ahithophel [אלשיך, חומת אנך].