Editor's Note: This story contains a correction. The McCrory campaign announced in a press release that it has filed a lawsuit, which WFAE reported. This is misleading. The McCrory campaign actually filed a request for a 20-day extension to file a lawsuit. An extension is not necessary. The campaign is well within the statute of limitations. The extension does not bind the campaign to file a lawsuit. Pat McCrory's campaign for Governor has sued has threatened to sue the groups behind an ad that attacks his records as mayor of Charlotte. The campaign is threatening to sue the television stations broadcasting the ad, as well. Such threats are relatively common, but actual defamation lawsuits over political ads are rare. It's a 30-second ad paid for by the Democratic Governor's Association and a group called Citizens for Progress. And yes, it's unflattering, like so many ads that have attacked McCrory during his political career.But this one crosses a line, says campaign spokesman Brian Nick "If you've been mayor of a city and you're proud of your work that you've done and you never would possibly take an action that wasn't in the best interest of the city and the people you represent, this ad says the opposite," says Nick. "It says that he took action to personally enrich himself." The ad certainly connects dots in a misleading way. It says McCrory was paid to sit on the board of directors for Tree.com. That's true - it was during the last year McCrory was mayor in 2009. Then the ad says, "(McCrory) used his position as mayor to lobby state government for millions in tax breaks for the company." It's true McCrory lobbied the state for tax incentives to keep Tree.com from moving to South Carolina. But that was several years before he joined the company's board and not after, as the ad might have you believe. So is that enough to win a defamation lawsuit? Raleigh attorney Hugh Stevens says "no." He's a leading expert in defamation law and was asked by backers of the ad to analyze the McCrory campaign's complaints. Stevens says courts have intentionally set the bar high when it comes to "political speech." "Partly on the theory - to quote Harry Truman - 'That if you can't stand the heat, get out of the kitchen,' says Stevens. "Part of running for office is that you expose yourself to a certain amount of criticism and some of it's fairly vitriolic." Meanwhile, the Republican Governors Association is running an ad painting McCrory's opponent - Walter Dalton - as "Bev Perdue's right-hand man." That's not true either, since in North Carolina the Governor and Lieutenant governor are elected separately and are responsible for totally different parts of state government. It's not exactly "anything goes" in the world of political attack ads, but Stevens says mounting a successful defamation suit is tough.