In the fall of 2007, as Mike Huckabee was surging in the Iowa polls, Mitt Romney's foundering presidential campaign dispatched a camera crew to Arkansas with the charge to produce one of the most brutal ads of the election cycle.

The final product — a withering spot that tied Huckabee to a 2003 murder committed by a serial rapist who was paroled while he was governor of Arkansas — never saw the light of day. But the unaired ad, obtained this week by BuzzFeed News, highlights a potentially potent line of attack on Huckabee as he considers a 2016 bid for the presidency.

The ad's existence was first reported in the 2012 book The Real Romney (and noted, then, by BuzzFeed News). The book's authors report that Alex Castellanos, then the Romney campaign's chief strategist, was aiming for an emotionally hard-hitting commercial that would have the same effect as the infamous "Willie Horton" attack ad on 1988 Democratic presidential candidate Michael Dukakis.

Others in the campaign, including Stuart Stevens, believed going after Huckabee so harshly would backfire. The operatives ultimately deferred to Romney, who spiked the ad, believing it would make him look "desperate."

The ad features an interview with the mother of the murder victim, condemning Huckabee's judgment and ruling him unfit to be president.

"This is my daughter," the mother says in the commercial. "She was pregnant with her first child. She was murdered by a serial rapist released early from prison in Arkansas. It was Mike Huckabee's intent that Wayne Dumond be released from prison. It's a pattern of bad judgment — very bad judgment. I don't know how you could trust that person with the highest power in our country."

On the screen at the end of the ad, white lettering appears against a black backdrop informing viewers, "Mike Huckabee granted 1,033 pardons and commutations, including 12 murderers."

Though this ad never ran, Romney did eventually produce a softer spot attacking Huckabee's extensive use of pardons to cast him as soft on crime. No doubt many of these cases are sitting in opposition research files belonging to Huckabee's prospective 2016 opponents — although it's unclear whether such a line of attack would carry the same force eight years later, at a time when many Republicans are rethinking their approach to criminal justice.

A spokesman for Romney declined to comment on the ad, while an adviser to Huckabee did not respond to a request for comment.