Just 20 percent of the negative ads airing in Iowa targeted Romney, even as part of an attack on multiple candidates, according to the Campaign Media Analysis Group. By comparison, 45 percent of the negative spots went after Gingrich—a statistic that explains, in part, why the former House speaker's poll numbers in the state plunged in the final days of the campaign.
Bailey points out that "none of Romney's 2012 rivals ran an ad solely taking on the former Massachusetts governor—a sign that they perhaps underestimated his rise in Iowa."
Buzzfeed has a good chart that breaks down how much the candidates and affiliated outside groups spent just on TV ads. Rick Perry's team spent $6 million--more than any other candidate--but the Texas governor seems to be headed for a fourth or fifth place finish this evening in Iowa. Rick Santorum, on the other hand, spent just $600,000, but is on track to place in the top three.