Anthony Weiner says he will soon decide whether to run for mayor of New York. As the former congressman weighs the pros and cons, he might want to keep an eye on Mark Sanford's comeback attempt in South Carolina.

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There is a lesson in Sanford's bid for Weiner, who in a round of recent media interviews offered uncertainty about whether the public had heard the last detail about the interactions he had online with women, which led to his downfall in 2011. The lesson: It's not just what's already out there that you have to worry about.

“I can’t say that [reporters] are not going to be able to find another picture or find another person who may want to come out on their own,” Weiner told RNN-TV on Wednesday.

If Weiner runs for mayor, he will be voluntarily putting himself back in the public sphere. And in doing so, he could open himself up to new attacks and scrutiny on an issue he hoped to put to rest when he resigned from Congress. Newly unearthed developments -- even if they are from before his resignation -- would put Weiner on defense in a campaign in which he will want to be talking about New York City, not lewd pictures he shared via Twitter or women he met online.

Sanford knows a thing or two about surprise developments hamstringing a comeback campaign. The former Republican governor fell from public grace in 2009 when he disappeared from the state, later revealing he left to visit his then-mistress and now fiancee. In his bid to return to elected office, Sanford has tried to put the episode behind him, apologizing and declaring that it's humbled him. I've "learned mightily" from my mistakes, Sanford said at a GOP debate.

End of story? Hardly. For one thing, Democratic outside groups have sought to implicitly remind voters about 2009. But more importantly, Sanford's divorce from ex-wife Jenny Sanford was thrust anew into the spotlight earlier this month, amid revelations she recently accused him of trespassing on her property. The episode was bad for Sanford not only because being accused of trespassing is hardly an ideal story line for a candidate for public office. It also reminded voters about the highly-publicized 2009 events that led to Sanford's divorce in the first place.

Making matters worse for the former governor, Jenny Sanford told The Washington Post that Sanford's sons were uneasy about appearing with their father and his fiancee on stage at a victory rally last month.

The difficulty with comeback attempts like the one Sanford is trying and Weiner might is that it's not just the stuff that is already out there that is problematic. New developments even tangentially related to the subject that brought about a politician's downfall can be even more damaging.