Jo-Ann Armao is a member of the editorial page staff.

As more sordid details emerge in the trial of former U.S. senator John Edwards (D), one question lingers: Why on earth did this man, who had so much going for him, risk everything — including a shot at the presidency of the United States — to have an affair with a woman best described as unpredictable? It’s hard not to wonder, as details are being recounted in a North Carolina courtroom of the frantic efforts to stash Edwards’s pregnant mistress from his dying wife (and the rest of the world) and how Edwards hit up a 101-year-old heiress for more money even as he was being investigated for campaign finance violations (for which he is now on trial).

The question hit home for me as I watched another politician — former D.C. Council member Harry Thomas Jr. (D), whose activities in running a suspect nonprofit I’ve covered for the past two years — try to explain to a federal judge last week how he came to steal hundreds of thousands of dollars meant to help needy children. “I took this money because it was a sense of entitlement,” Thomas told U.S. District Judge John D. Bates. “I went astray, and I lost my way.”

I just can’t make sense of this explanation. Much like Edwards (who had looks, smarts, money and a loving family), Thomas had great advantages. Twice elected to the council seat that had been held for years by his father, Thomas was a rising political star much liked for teaching baseball to young people, his easy charm with voters and his advocacy for the downtrodden. Some saw him as a possible mayoral candidate. Why would he jeopardize that promising career for a new Audi, golf at Pebble Beach and a pair of leather chaps?

Equally mind-boggling is how his self-dealing began within weeks of taking office in 2007. Federal prosecutors have detailed how Thomas went to a group offering an arts program for youths and promised a $60,000 government grant if it would kick back $15,000 to him. Apparently emboldened by that success, Thomas — drawing others into his scheme — helped arrange for $392,000 in city monies earmarked for “youth baseball programs” to go to a nonprofit organization that, in turn, funneled $306,000 back to Thomas. While he was surreptitiously stealing these public funds, Thomas was publicly bemoaning the city’s budget issues and criticizing the then-mayor for his supposed lack of ethics.

When Thomas was caught, he tried to bully and bluff his way out, thinking, like so many officials snagged in scandal, that his position, pedigree and politics would protect him. At first, Thomas dismissed questions about the phony charity that bore his name as a “very useless fishing expedition.” He visited The Washington Post’s editorial board, with his attorney, to express indignation that his integrity had been questioned.

He promised to be “as open and transparent as possible,” but he fought efforts by the city’s attorney general, then Peter J. Nickles, to get information and accused Nickles of playing politics with his office. After the District filed a civil suit to reclaim money that it had determined had been stolen, Thomas promised to prove his innocence, saying: “I’m willing to risk everything I have.”

Even when Thomas reached a settlement with the city to repay hundreds of thousands of dollars, he continued to insist that he had done nothing wrong. It was a little like denying you are having an affair after a National Enquirer reporter has caught you leaving your mistress’s hotel at 2:40 a.m.

The years of evasions, denials and outright lies make it hard to know whether these men can be believed when they say they are sorry. Unlike Edwards, who says he broke no laws even as he made mistakes, Thomas pleaded guilty to two felonies. “What I did was wrong, and I broke the law,” Thomas told the judge last week. His voice cracked as he talked about what his late father would say and the shame of hearing his mother plead for leniency. When Bates announced a sentence of 38 months, his mother’s ramrod posture grew even stiffer.

A similar moment of pain was visible in Greensboro, N.C., last week, when Edwards’s oldest daughter fled the courtroom in tears to escape further details of how her father humiliated her mother.

In that courtroom emerged the best explanation for why these public men committed such destructive acts. A speechwriter who prepared Edwards for the questions that would follow his eventual confession testified that, if reporters asked why he did it, he should be honest and answer: “I didn’t think I would get caught.”