For voters hoping the state’s campaign for the U.S. Senate will focus on issues and not personal attacks, Democrat Tom Allen’s call for outside groups to skip the negative advertisements was welcome news. Incumbent Sen. Susan Collins immediately took his challenge a step further and said she’d tell the Republican Party not to run any television or radio ads if Rep. Allen would do the same of the Democratic Party.

“If you plan to attack Senator Collins – don’t,” Allen said in a press release. Instead, he said, ads should focus on the issues and his record, and should be positive.

Such pledges, while they sound good, are virtually meaningless because the candidates cannot communicate or coordinate with these outside groups. So, a candidate can condemn attack ads all he wants, but he can do little to stop such ads, and once an ad has aired, the damage is usually done.

Negative attack ads are often the work of so-called 527 groups, named for the tax code section under which they are formed. Because they don’t have to register as federal political committees they do not have to abide by contribution limits or reporting requirements.

On the right, the best known 527 is likely Swift Boat Veterans for Truth, the group that ran ads questioning Sen. John Kerry’s military record in Vietnam. On the left is MoveOn.org, which may be best known for its ad campaign calling the top U.S. commander in Iraq, Gen. David Petraeus, “General BetrayUs.”

In the 2004 presidential campaign, President Bush criticized the Swift Boat ad – after it had been taken off the air. He said the 527s were bad for the system.

Last summer, a group called Americans Against Escalation in Iraq sent out pictures showing Sen. Collins with blacked-out teeth, calling her toothless on Iraq. Rep. Allen did not condemn the ads, saying now that his campaign was just getting organized then.

Last month, presumptive Republican presidential nominee John McCain implored the North Carolina Republican Party to not run a television ad tying two Democratic gubernatorial candidates to Barack Obama and his controversial former pastor, the Rev. Jeremiah Wright. In a letter to Linda Daves, chairwoman of the state’s Republican Party, Sen. McCain said the advertisement “degrades our civics and distracts us from the very real differences we have with the Democrats.”

The party aired the ad, which included clips of the Rev. Wright condemning the United States during sermons, anyway.

Recent campaigns show that denouncing such ads does little to stop independent groups from airing them. Having a substantive conversation with Mainers about a change in direction, as Rep. Allen says he wants, will take more than well-meaning but largely empty pledges.