WASHINGTON (Reuters) - Washington operatives call it "drawing contrasts." Voters call it "slinging mud."
Whatever the term used, the most expensive election in U.S. history is likely to feature an unprecedented amount of negative advertising as Republicans and Democrats vie for control of the White House and Congress, campaign officials told the Reuters Washington Summit.
The attack ads could be driven in part by laws that aim to keep elections clean by separating campaigns from interest groups, according to the spokesman for a Republican group that plans to spend $300 million this year.
"It's difficult for any outside organization to run effective positive ads," said Jonathan Collegio, communications director of American Crossroads, one of several "Super PACs" formed to take advantage of loosened campaign-finance laws that allow unlimited donations to such groups.
Groups that operate separately from campaigns aren't solely responsible for the surge in negative ads.
President Barack Obama's campaign is attacking Republican rival Mitt Romney's record as a private equity executive and as a one-term Massachusetts governor.
Obama's fellow Democrats in Congress, who had to defend Obama's unpopular health care overhaul in 2010, plan to run against equally unpopular ideas that Republicans have tried to put in place during the past two years.
In politics it is easier to play offense than defense, said U.S. Representative Steve Israel, who as head of the Democratic Congressional Campaign Committee is leading efforts to win back the House of Representatives.
"We're going to make this a referendum on Republican choices," he said.
Republicans and their allies, meanwhile, are primed to spend well over $1 billion attacking Obama and other Democrats.
"You'll see more of a message about voting against President Obama because his policies are failing the country," Collegio said.
The ratio of negative to positive ads may not differ substantially from previous election cycles, but two factors are likely to make 2012 seem nastier: the volume of advertising that will run in key states, and the rise of Super PACs along with their nonprofit sister groups, which do not have to disclose their donors.
The groups allow candidates to leave much of the dirty work of negative ads to outside allies.
Restore Our Future, a Super PAC allied with Romney, has spent $47.4 million on negative ads so far, first to tear down Republican rivals such as former U.S. Senator Rick Santorum during a bruising primary season, and more recently to target Obama. The group has spend just $6.8 million on ads supporting Romney.
In the same vein, Priorities USA Action, a Super PAC that supports Obama, has spent $10.1 million attacking Romney and nothing on ads boosting Obama.
Voters often say they don't like negative ads, but political analysts say they deliver results. That seems to be the case this year.
A Wall Street Journal/NBC News poll released on Wednesday found that voters in battleground states view Romney less favorably than they did before Obama and Priorities USA launched a negative ad blitz targeting Romney's business career.
Voters in those states also hold a more negative opinion of Romney's career with the private equity firm Bain Capital than voters in the rest of the country, the poll found.
"It's clear that the ads are having an impact," said Bill Burton, who heads Priorities USA Action.
Existing election laws also may be a factor in promoting negative advertising.
Outside groups are not allowed to work directly with the candidates they support, and because of that may face heightened scrutiny for ads highlighting the attributes of a particular candidate.
When American Crossroads ran an ad backing Ohio U.S. Senate candidate Rob Portman in 2010, the state's Democratic Party filed a complaint with the Federal Election Commission.
The complaint ultimately was dismissed, but "it created a headache that no one wanted to have," said Collegio, adding, "In a weird way, the campaign laws encourage negative and contrast advertising."
That's hogwash, said Guy Cecil, who as chief of staff of the Democratic Senatorial Campaign Committee is leading his party's effort to retain control of the Senate.
There's no reason Crossroads couldn't film someone such as Montana Republican Senate candidate Dennis Rehberg speaking at a public event, for use in an ad, he said. Instead, the Super PAC has run ads critical of Democratic incumbent Jon Tester.
"It's not hard for them to run positive ads," he said. "You don't think Crossroads could access Dennis Rehberg's public schedule?"
Indeed, Crossroads said on Wednesday it would spend $184,000 airing an ad praising New Mexico's Republican Senate candidate Heather Wilson, an Air Force veteran.
The U.S. Chamber of Commerce has also run ads praising Republican candidates like Orrin Hatch in Utah and Linda Lingle in Hawaii.
Overall, 70 percent of the ads in this year's presidential race have been negative, according to the Wesleyan Media Project. In 2008, 9 percent were negative.
In coming months, Priorities USA will tie Romney to Republican ideas such as restricting access to contraception, cutting back stem cell research and scaling back the popular Medicare health plan for the elderly, Burton said.
He said he had little choice given the expected Republican onslaught.
"They're going to be nasty, and they're going to be dishonest, and the best we can do is make sure that we are answering point by point what they're saying about the president and what they're saying about Mitt Romney," he said.
If there's any silver lining, it's that both sides say they will steer clear of personal attacks.
"If a negative ad is running a message about how somebody had three ex-wives, and that kind of thing, that to me is very different than if you ran an ad about how somebody supported the last three tax increases," Collegio said.
Additional reporting by Alex Cohen; Editing by Ros Krasny and Eric Walsh