New York City was shocked on Tuesday when mayoral candidate Anthony Weiner admitted that in 2012 he engaged in racy online conversations and sent explicit photos to a woman -- a year after he resigned from Congress because of similar misbehavior and promised to change his ways.
Weiner's confession, forced by a website that published details of his dalliance, is threatening to derail what to this point had seemed like one of the most remarkable political comebacks ever.
The candidate, who was narrowly leading the Democratic mayoral field by three points in a July 15 Quinnipiac University poll, insists he's staying in the race, despite calls by newspaper editorial writers for him to drop out.
"I hope are willing to still continue to give me a second chance," he said at a news conference.
So far, the public has been willing to do that. Quinnipiac found that more than half of Democratic primary voters thought it was OK for Weiner and former Gov. Eliot Spitzer, another candidate with sexual indiscretions in his past who is running for city controller, to seek office again. But will they forgive Weiner yet another time?
Quite possibly, yes, if psychological research about the nature of forgiveness and studies of public attitudes about politicians' private morality is any guide.
"Americans have an amazing depth of forgiveness for politicians," says Frank Farley, former president of the American Psychological Association and a Temple University psychologist who studies political behavior and human emotions.
He notes that there are plenty of leaders whose reputations survived sex scandals, from former President Bill Clinton to former South Carolina Gov. Mark Sanford, who left office in 2010 after admitting to an extramarital affair, only to resurface this year and win election to Congress.
"Look at Clinton," Farley says. "He managed to land on his feet, and he's now probably the most popular politician in the world."
Our brains have been wired by evolution with the capacity to forgive. A 2001 study by British researchers, who watched subjects' brains with MRI scanners, found that forgiveness is a complex activity that involves multiple parts of the brain, in particular the posterior cingulate gyrus deep inside our brains. We learn to use that equipment.
"The evidence is clear that forgiveness can be taught," Farley said.
And to an extent, we may be programmed to forgive and forget. A study by University of Chicago behavioral scientist Eugene Caruso, published in the Journal of Experimental Psychology General in 2010, found that we're more likely to view future misdeeds more harshly than identical transgressions that have occurred in the past.
In Caruso's experiment, subjects were more upset when they learned that a cold drink vending machine automatically would raise prices the following month when the weather got hot, compared to another group who was told that the machine had been set to do that in the past.
We have a tendency to forgive, even though it may not always be in our interests. In a 2010 study, Florida State University psychology professor Jim McNulty found that newlyweds who reported that they'd forgiven a spouse for a transgression on a particular day were 6.5 times more likely to report the following day that their partner had done something negative again.
In other research, McNulty found that those who forgave partners who habitually behaved badly tended to feel worse over time. Forgiving people who did bad stuff, he concluded, didn't necessarily improve their behavior.
Indeed, we seem to hold politicians by a looser standard than people we actually know intimately, such as our own spouses.
A 2008 Gallup poll found that 64 percent of Americans wouldn't be able to forgive their husbands or wives for infidelity, compared to 33 percent who would. Interestingly, though, only 36 percent of Americans say that if they were married to an elected official, they would stand next to the person on a podium while he or she was answering questions about an affair, as Weiner's wife Huma Abedin did on Tuesday.