Herman Cain, who suspended his presidential campaign this weekend after cascading reports of personal failings, is the exception. American voters are increasingly tolerant when it comes to private behavior.

Three of the last five Republican presidential nominees have been divorced. President Bill Clinton survived, even flourished, after revelations of a sexual dalliance with an intern, and Republican Sen. David Vitter of Louisiana was re-elected even after disclosures that he frequented a prostitute.

The acid test of this growing openness may be the new Republican presidential frontrunner, Newt Gingrich.

His personal past is messier than most; he’s on his third marriage, left his first two wives when they were in poor health and while having affairs.

Also, his version of events is replete with gaps, changing and contradictory stories; both of his two former wives have questioned his moral character.

Finally, he is the front-runner of a party in which a sizeable chunk of the base consists of family-values conservatives who will have to decide between Gingrich’s rhetoric and his past.

When the former House speaker first announced his intention to run for the presidency in May, there were stories detailing his past transgressions; his candidacy floundered and coverage ceased. In the past few weeks, as other challenges to the then-front-runner, former Massachusetts governor Mitt Romney, collapsed, the Gingrich candidacy soared in the polls.

A centerpiece of Gingrich’s wide-ranging message is a call to restore moral values and stop President Obama’s “secular-socialist machine,” the subtitle of one of his recent books.

The return to the spotlight means renewed scrutiny by the media and his opponents. Two recent episodes crystallize the stakes and challenges.

The first was a letter from his daughter, Jackie Cushman Gingrich, that was published on a website. She knocked down recurring reports that in 1980, her mother was dying of cancer, her father visited the hospital to discuss the terms of their divorce. Jackie Gingrich says her mother is alive and, in fact, was herself the one who initiated the divorce proceedings well before she went into the hospital for cancer surgery.

The other was an open letter a few days ago to Newt Gingrich from Richard Land, an influential leader of the Southern Baptist Convention. He called on the candidate to express a mea culpa for his personal past before a pro-family venue.

“You need to make it as clear as you possibly can that you deeply regret your past actions,” Land wrote. “Promise your fellow Americans that if they are generous enough to trust you with the presidency, you will not let them down and that there will be no moral scandals in a Gingrich White House.”

The record complicates his daughter’s vindication and the Land challenge. In 1985, five years after the divorce, Gingrich’s first wife, Jackie, spoke to several reporters. She confirmed the story that her husband came to see her at the hospital post-surgery to talk about a divorce that he had initiated. The accounts of both Gingrichs were then confirmed in a Washington Post interview that is at odds with the current contention of their daughter.

“He can say that we had been talking about it for 10 years but the truth is that it came as a complete surprise,” Jackie Gingrich, who met her husband when she was his high school geometry teacher, said in that interview.