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Evan Vucci, File, Associated Press
FILE - In this Dec. 28, 2011 file photo, Republican presidential candidate, Rep. Michele Bachmann, R-Minn., meets with patrons at the Nodaway Diner in Greenfield, Iowa. So much for playing nice with each other. The Republicans vying for their party’s presidential nomination have set aside the pretenses of alluding to their rivals or letting supporters unleash the most abrasive criticism. No, they’ve largely abandoned the practice of nimbly pointing out difference in their records. Now, it’s in-your-face comparisons. Iowa Nice has been replaced by Iowa Nasty.

CEDAR RAPIDS, Iowa — So much for Iowa Nice. It's more like Iowa Nasty.

In a state whose Midwestern civility usually extends to politics, the Republican presidential campaign has become an acerbic affair. Negative ads fill TV and radio. Attacks are all over the Internet and in material stuffed in mailboxes. Many of the candidates are bashing each other with abandon.

It's a reflection of the crowded GOP field and the volatile race to emerge as the Republican challenger to President Barack Obama in November. To the dismay of many voters, it's also probably only going to get worse when there are fewer candidates and the contest moves to New Hampshire, South Carolina and beyond.

"If they go negative, they aren't getting my vote," says Ginger Allsup, a 45-year-old Oskaloosa bakery worker.

That's a risk campaigns in Iowa are willing to take, given the high stakes and state of the race ahead of Tuesday's caucuses that kick off the fight for the GOP nomination.

Only three candidates typically make it out of Iowa with enough momentum and money to continue. Polls are showing that most hopefuls are bunched tightly behind former Massachusetts Gov. Mitt Romney. Desperate to break from the pack, they're whacking away in hopes of sinking opponents and wooing undecided voters.

Usually, presidential candidates and their allies take care to be congenial in Iowa, which has a record of rewarding candidates who stay above the fray. It's a state where campaigns seek to make positive first impressions by promoting their own policies and offering subtle comparisons.

By the time New Hampshire comes around, the field usually has narrowed and those left standing try to differentiate themselves even more, in a sharper and often more personal tone. It only escalates from there when voting turns to South Carolina, which has a long history of go-for-the-jugular politics.

But Iowa is different this year.

It's partly because of a Supreme Court decision that allowed unions, corporations and individuals to spend unlimited amounts of money to advocate for the election or defeat of candidates. As a result, new outside groups, known as super PACs (political action committees), that are aligned with the candidates sprang up. These groups have paid for an avalanche of hard-hitting TV and radio ads, as well as aggressive literature in mailboxes and harsh messages online.

What about the candidate? They're hardly holding their tongues. Sometimes, they're using language that Republicans often reserve for Democrats

"She doesn't like Muslims, she hates them, she wants to go get 'em," Texas Rep. Ron Paul said about Minnesota Rep. Michele Bachmann. "Dangerous" is how Bachmann describes Paul's foreign policy.

In other cases, they use humor to try to blunt the force of the attacks.

Asked about Newt Gingrich's failure to get on the Virginia ballot, Romney likened the former House speaker's political operations to an out-of-control chocolate factory from a half-century-old "I Love Lucy" episode.

"Cute" was Gingrich's reply.

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.