FORTUNE — In the aftermath of President Obama’s victory over Mitt Romney, there has been a lot of attention paid to how the Obama campaign successfully defined Romney as an out-of-touch corporate raider. And most of the credit has gone to Obama campaign boss Jim Messina, who made a “grand bet” to saturate the summer airwaves with anti-Romney ads while the GOP nominee was still recovering from a drawn-out primary battle.

But this victory narrative misses a very large point: Messina’s gamble was enabled by Newt Gingrich.

The Romney campaign was well aware that Bain Capital would become a major issue in the general election. After all, the late Ted Kennedy had created the blueprint in his 1994 Senate race against Romney (the only time Romney had run against a Democrat, and lost).

What it didn’t expect, however, was that one of its primary opponents would bring the issue to the fore. After all, John McCain didn’t touch the subject four years earlier — with the only mention of Bain coming from Mike Huckabee, who suggested that Bain’s ownership of Clear Channel was why he had failed to secure endorsements from some of the company’s conservative radio hosts.

“No one in the campaign believed that Republicans would attack business enterprise in a primary contest,” explains a Romney campaign consultant who declined to be identified. “That was, in hindsight, a big mistake.”

The first jabs came from Rick Perry, who accused Romney in an early January debate of being a “vulture capitalist.” But the heavy artillery was manned by Newt Gingrich, who began accusing Romney of “looting” companies. More importantly, a super PAC supporting Gingrich released a 28-minute video titled “When Mitt Romney Came to Town” — full of ominous music and tales of woe from workers at companies acquired by Bain Capital.

Never mind that much of the video was misleading, or that Gingrich would later try to disassociate himself from the tape. The negative seed was planted, particularly in the minds of independent voters who had never before heard of Bain Capital or private equity.

If even stalwart Republicans like Newt Gingrich had a problem with what Romney did at Bain Capital, then it would be much harder to dismiss the subsequent Obama campaign attacks as partisan, anti-business rhetoric. Instead, Messina’s “grand bet” was really just sweetening an existing pot — reinforcing a caricature first drawn by Gingrich. And the Romney campaign had lost complete control of its own candidate’s image.

“By late summer there wasn’t even one particular thing he did at Bain that really mattered anymore,” the consultant says. “In fact, you didn’t even have to say Bain. People just instinctively believed that he had outsourced people, fired people, not cared about people. It wasn’t about what had actually happened, or about policy. It wasn’t substantive. But it got the job done.”

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