This weekend marks the first negative TV advertising in the two early-voting states as the campaign headed into the critical weeks before the first voting, with an independent group's claim that the former Massachusetts governor has flip-flopped - a sometimes crippling charge in presidential politics. Analysts say similar negative ads are likely against his chief GOP rival, Rudy Giuliani, whose positions on gun control and immigration are markedly different from those he espoused as New York mayor.
The anti-Romney ad campaign, by a Republican group that supports abortion rights, is fairly modest in scope. But it may open the door to bigger ad buys targeting other candidates and topics, several campaign veterans said.
"This will be the beginning of it," said Patrick Griffin, a Manchester-based advertising executive who handled President Bush's 2000 media effort in New Hampshire.
Given the pending ad against Romney and the confrontational tenor of Wednesday's Republican debate in Florida, Griffin said, the top campaigns must be ready to launch hard-hitting ads the instant they decide the benefits outweigh the risks. "You can be sure there are scripts written and, very likely, spots produced," he said.
And if not television, then radio. On Thursday, a Republican group that advocates for gay rights launched a 60-second anti-Romney radio ad criticizing his tax record.
Negative ads are certainly possible in the Democratic contest as well. But strategists say they are not surprised to see them first in the Republican race, where front-runners Romney and Giuliani have left a long evidentiary trail of their changed positions on key issues.
"It's a target-rich environment for negative ads," said Dante Scala, a political scientist at the University of New Hampshire.
Accusations of flip-flopping have animated campaigns for years. They proved especially damaging to Democratic presidential nominee John Kerry in 2004, and they have dogged Romney and Giuliani this year.
Thus far the accusations have arisen only in debates and news accounts, not in potentially powerful TV ads that often employ ominous music and grainy black-and-white or slow-motion images. And while campaign ads have saturated the Iowa and New Hampshire airwaves for weeks, they have been mostly upbeat, biographical spots.
That will change this weekend when the group Republican Majority for Choice starts its ads - in Iowa and New Hampshire newspapers and TV spots - calling Romney a flip-flopper on abortion.
The ads' potential impact is unclear. Romney repeatedly has acknowledged being an outspoken supporter of abortion rights until he changed his mind a few years ago.
"I don't know how many times I can tell it: I was wrong," he said in Wednesday's debate. Voters seeking candidates who are "not willing to admit they're ever wrong," he said, will "have to find somebody else."
The major threat to Romney would be TV ads suggesting his conversion was politically motivated to appeal to Republican primary voters. Among the rivals already raising the issue is Arizona Sen. John McCain, who has said Romney's biggest challenge "will be convincing Republicans he has principled positions on important issues."
Questions about gay rights also might provide grist for anti-Romney ads. When he unsuccessfully challenged Sen. Edward M. Kennedy, D-Mass., in 1994, Romney vowed to outdo the senator in championing the rights of gay men and lesbians in the workplace. "We must make equality for gays and lesbians a mainstream concern," Romney said at the time.
He never supported gay marriage, and he now highlights his support of "the traditional family" and a constitutional amendment to ban on same-sex marriages.
Some Republicans feel Giuliani is equally vulnerable to charges of flip-flopping if a televised feud begins.
As mayor, Giuliani sued gun makers and distributors, backed a federal assault-weapons ban and once described the National Rifle Association as extremist. He no longer holds those views, saying the terrorist attacks of 2001 changed his thinking about weapons and personal protection. He was quoted in 2002 and 2004, however, still staunchly supporting gun control.
Giuliani promises to crack down on illegal immigration, a message also at odds with his record as mayor. In 1996 he said there are times "when undocumented aliens must have a substantial degree of protection" to feel safe sending their children to school, reporting crimes and seeking medical treatment.
Such policy shifts by Giuliani and Romney are ready-made for negative ads, campaign strategists say, but the strategy carries risks. New Hampshire's all-important independent voters are especially leery of one-sided claims, and "there's a danger it can backfire," said Dean Spiliotes, who writes a nonpartisan political blog in New Hampshire.
Moreover, several analysts said, a serious Romney-Giuliani spat could catapult another candidate, such as McCain, to the top.
For all those reasons, it is possible that most or all of the early negative ads will be aired by independent groups, such as the one now targeting Romney on abortion. If the candidates decide to launch their own attack ads, "I think it's likely to happen in the last week or two," said Andy Smith, a pollster at the University of New Hampshire.
Meanwhile, candidates will anxiously monitor polls, campaign event crowds and other signs that their campaign is going up, down or nowhere. Ultimately, at least one candidate will decide negative ads are worth the risk, said Michael P. Dennehy, McCain's New Hampshire-based national political director.
"No candidate wants to be the first to go negative," Dennehy said in an interview. "But it will be done, mark my word. It's just a question of when."