WASHINGTON - Pretty much by definition, a man who can be described as a cad is not a wholly admirable human being. There are, however, cads whose behavior shows a certain panache, a sense of humor and a genuine, if flawed, humanity.
John Edwards' caddishness, it appears, has no redeeming social or political value. He's just a bad cad.
According to reports, a former close Edwards aide has shopped a book proposal in which he claims that the former presidential candidate is indeed the father of his mistress' 19-month-old daughter - which Edwards has categorically denied.
The aide, Andrew Young, is in a position to know: When the affair was revealed, Young allowed himself to be named as the child's father. That was a lie, Young now says, intended to salvage what was left of Edwards' political career.
But that's not the worst of it - and certainly not the tackiest. Young claims that Edwards promised the mistress, Rielle Hunter, that he would marry her after his wife Elizabeth had died of her inoperable cancer. And that they would have a rooftop ceremony in New York. And that there would be music by the Dave Matthews Band.
That may be the most caddish thing I've ever heard.
I used to like John Edwards a lot. I liked the fact that all his artifice and ambition were right there on the surface. I liked his combativeness, his skill as a debater, his quick intelligence. I especially liked the story of his family - the long marriage that had survived so many cruel tests.
So when reporters from the National Enquirer cornered Edwards at the Beverly Hilton, where he had arranged a secret meeting with Hunter and the baby, I was stunned. I knew that married men sometimes stray, especially married men who are rich, famous and handsome. I also knew that cancer can be brutal on marriages.
But he hadn't just betrayed his wife, he had betrayed the staffers, volunteers and voters who gave him their toil and trust. He had betrayed the Democratic Party and, potentially, the nation. What if this walking scandal had somehow won the nomination?
In the course of what Young describes as a subterfuge to conceal Edwards' paternity, two of the former senator's campaign donors were tapped for funds that went to Hunter as what would appear to be hush money. Edwards is being investigated for possible campaign-finance violations, though I think it will be hard for the law to lay a glove on him.
But looking forward, with his mistress, to the day when Elizabeth would die? Planning a post-funeral wedding? Choosing the rock band? Even if all this was just a fairy tale meant to reassure Hunter and keep her quiet, I can't have any "like" for John Edwards anymore. The forgivable kind of cad could never do such a thing. Only the worst kind would.
• Eugene Robinson's e-mail address is firstname.lastname@example.org.