Iowa caucuses: GOP race gets nasty as contest nears
He then issued a challenge as he visited a chocolate factory the day after Romney's poke: "Here I am in the chocolate factory. And now that I have the courage to come to the chocolate factory, I hope Gov. Romney will have the courage to debate me one on one and defend his negative ads."
Candidates are being harder on some rivals than others as they look to peel off support from certain blocs.
"I am a consistent conservative. I have always been pro-life. I have always been pro-traditional marriage. I have always been a fiscal conservative. I have never been for global warming," Texas Gov. Rick Perry said this past week in response to a voter's question. He then added, "I'm glad you gave me the opportunity to reflect my differences with Mitt."
Perry was much sharper hours later as he fought for support from Christian conservative voters also being courted heavily by former Pennsylvania Sen. Rick Santorum.
Said Perry: "He is what I call a serial earmarker," referring to the special spending projects that members of Congress seek.
Santorum, who is rising in polls and may end up being Romney's prime challenger in Iowa, said Romney had no track record of success. "In fact, he's only run as a moderate or a liberal," Santorum said.
Running ahead in polls, Romney took care not to initiate attacks and only weighed in when asked questions. But he did give pointed responses.
"I don't think Ron Paul represents the mainstream of Republican thought with regards to issues, particularly in foreign policy,' Romney said, seeking to marginalize his closest pursuer in most polls.
There's a reason candidates are assailing each other: It can work.
Consider Gingrich's up-and-down December.
He was flying high in polls at the start of the month. Then he was pounded by at least $4 million in negative TV ads in Iowa, most run by Romney allies and some by Paul's campaign. The ads cited both personal flaws and professional missteps.
Mailings described him as "as a 30-year Washington insider" who has "taken both sides on core Republican issues." His infidelity is highlighted in emails circulating among conservatives. In addition, a video he once recorded with then-House Speaker Nancy Pelosi, D-Calif., urging action on climate change blankets the Internet.
At campaign events, Bachmann, Paul and others spread those same messages.
"I had been leaning toward Newt," said Jean Fredsall, a 67-year-old retired social worker from Cedar Rapids. "But then I was reminded of his baggage."
But negative advertising also can backfire, particularly in a crowded field in Iowa.
In 2004, former Vermont Gov. Howard Dean and then-Missouri Rep. Dick Gephardt were the front-runners to win the Democratic nomination. Looking to seal the deal, each ran blistering ads just before Iowa voted. Both ended up losing voters and the nomination. Massachusetts Sen. John Kerry and then North Carolina Sen. John Edwards got the coveted tickets out of the leadoff caucus state.
The lesson: Those who run negative ads risk driving up their own negative perceptions in voters' minds.
Republican Mike Huckabee probably was mindful of it four years later.
Rising in the polls just before the caucuses, the former Arkansas governor was the target of criticism. But while pundits called for him to go on the attack himself, the most Huckabee did was tease a negative ad during a news conference. Then, he shelved it before it ever ran.
"It's not worth it," he said, adding: "It's never too late to do the right thing."
Iowans ended up rewarding him with a caucus victory, though John McCain captured the nomination.
Four years later, that lesson seems lost.
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