Negative advertisements are a favored subject for righteous indignation among editorial columnists and political pundits. Many assume the ads are used only for baseless smears that distort the record. The overlooked truth, though, is that negative ads can have a dramatic and devastating impact, sometimes against the very candidate who paid for them.

That seems to be the case in Minnesota, where after almost a year of the nastiest, most personal U.S. Senate race in the country, Republican incumbent Norm Coleman announced last week he would unilaterally suspend his negative campaign advertisements for the remainder of the race. The trouble is, it may already have cost him a once-comfortable lead.

Recent polls show Democrat Al Franken, the former Saturday Night Live funnyman who once fronted liberal Air America Radio, leading Coleman by a small margin, thanks largely to an independent electorate divided between the two major party candidates and Independence Party candidate Dean Barkley. And it has been Coleman's favorability ratings that have plummeted, not Franken's, as the senator's negative ads have flourished.

In the latest Minneapolis Star-Tribune poll, just 38 percent of respondents said they had a favorable impression of Coleman's job performance, the lowest he's ever registered in the survey. In May, 45 percent of Minnesota voters though positively of Coleman's job performance. And according to the latest poll, 56 percent call ads run against Franken by Coleman and the National Republican Senatorial Committee unfair attacks; 42 percent say the same thing about ads Democrats are running attacking Coleman.

Some political watchers suggest Minnesota just isn't the place for negative advertising. "In general, Minnesota culture frowns on open conflict, hostility and rudeness, a mindset we call 'Minnesota Nice,'" said Chris Federico, a political scientist at the University of Minnesota. The state's political culture "puts a strong emphasis on clean government and the avoidance of anything that would appear dirty. Negative campaigning runs afoul of both 'Minnesota Nice' and this moralistic attitude toward politics."

While others may disagree that anyone violated the "Minnesota Nice" code, observers do agree that the landscape required drastic measures. With Barack Obama leading the presidential contest in the state and with Democrats funneling millions into two competitive House races there, Coleman's decision may have been made in hopes of casting him in a new and favorable light.

"Coleman realized he had to change the tone of the campaign if he had a chance to be successful," said Blois Olson, a Minnesota political analyst. "He's got so many variables moving against him right now, so he's got to do something fundamentally different."

Attacking Franken, a wealthy comedian prone to dirty jokes who barely lived in Minnesota until deciding to run for the seat, isn't hard. And while last-minute attacks rarely sink in, Olson said Coleman was actually too successful too early. Assaults on Franken's tax records, on a column he wrote for a men's magazine and on myriad tales of crass and inappropriate language used in the pursuit of humor started as early as the spring.

"They got everything about Al Franken out really early. If some of the stuff that they were going to attack Franken on hit him now, it would be a totally different story. It would be game-changing," Olson said. "The negative ads against Franken were running for so long that they had done all the damage they could."

Coleman's attacks focused largely on Franken's personal and business background, tagging him as a tax cheat Hollywood liberal with a dirty mind. Franken's attacks focused more on Coleman's public record, including government oversight, infrastructure and, more recently, the economic bailout proposal, which Franken came out against. "The issues Franken was attacking on were far more relevant," Olson said.

Franken has no intention of pulling down his own ads. "The fact is that there are honest differences between Al Franken and Norm Coleman, and we're going to continue to point out those differences so that voters can see they have a clear choice between change and more of the same," said Colleen Murray, a spokeswoman for the Franken campaign. "It's not time for political stunts to distract from the fact that Norm Coleman has a negative record and his misleading attack ads were backfiring."

Coleman's negative campaign "wasn't getting him anywhere in the numbers. The nastier he got, he kind of looked like McCain did last week: The economy's in the tank, and voters said, 'This isn't what we want to hear about.'"

Indeed, the economic plunge played a major role in the decision to suspend the ads, said Cullen Sheehan, Coleman's campaign manager. "In this environment, in this time when people are nervous and they have a lot of fears, it doesn't help to play into that with negative campaigns," he said. "Part of the decision was that Norm didn't have any interest going back to Washington for six years based on voters thinking he's the lesser of three evils. He wants people to vote for him and not against the other guys."

In general, focusing a campaign on an incumbent's record can be a dangerous way to run a campaign. But this year's Senate race is a unique instance in which a largely positive campaign might have an effect.

Franken's message has largely been one of change, and that's a successful way to urge voters to fire an incumbent. But voters have a third choice, in Barkley, that could cost both candidates. The Independence Party candidate, who served briefly in the Senate after the death of Paul Wellstone in 2006, is pulling almost a third of independent voters to his side, polls show, and about an even number of voters from Coleman and Franken's party bases.

Those who buy into Franken's message that the incumbent should get the boot should be voting for the Democrat. But because of Franken's own baggage, voters who want to vote against Coleman but not for Franken have a happy medium in Barkley. That helps Coleman by depriving Franken of voters who despise Republicans but can't swallow a six-year Franken term, and it helps Franken by depriving Coleman of voters disgusted with the Democrat but less willing to vote Republican.

But just because Coleman isn't running negative ads doesn't mean no one is. The National Republican Senatorial Committee has launched their own barrage of assaults against Franken, including a new one on Tuesday, forcing Coleman to call on the committee he is rumored to have ambitions of running to pull down the ads. "While I can only control those ads that I must personally approve, I am calling on this group to immediately pull down this ad," Coleman said in a statement Tuesday. "I want the people of Minnesota to hear the positive record that we've built together, and the vision of a stronger country, with more jobs, energy independence and quality, affordable health care for all Americans. These negative ads must end."

Because of the third-party ads (Democrats' senatorial committee has been up for months with their own ads hammering Coleman), there is a danger that Coleman could lose credit for his apparently altruistic act. "Nobody distinguishes between the ads you're running and the ads other people are running on your behalf," Olson said. It's something Coleman manager Shaheen acknowledges: "Sometimes that distinction can be difficult, but ultimately we're responsible for the ads that say, 'I'm Norm Coleman and I approve this message,'" he said.

Coleman is currently trailing Franken in the latest Real Clear Politics Average, but no matter the outcome, the race will provide future campaigns with important lessons about negative advertising. The early ads attacking questionable moments in Franken's past were effective, but grew stale over time. And when voter concern focused almost completely on the economy, the attacks provoked a backlash.

Negative advertising remains a tool that can be used to great effect. But if voters begin blaming the candidate running the ad, the opposite effect can devastate a campaign. Coleman backers can only wait to see whether his campaign caught the mistake in time.