The defining moment in Shawn Flaherty's run for the state House fell one week ago today. He and his wife, Debbie, called their 16-year-old daughter to the living room of their Fox Chapel home and told her she has a 14-year-old sister somewhere.

The quick explanation -- that is to say, the one Mr. Flaherty's political opponents have in an opposition research report scraped out of old court files -- is this:

In 1992, after a period of marital strife, Mr. Flaherty became romantically involved with another woman. The woman became pregnant and sued for child support, which the Flahertys paid once paternity was established.

The child's mother married two years later and her husband adopted the girl.

They live somewhere in the state's northeast. Doubtless, someone in politics is looking for them at this moment.

"We sat down and told her. I guess kids are pretty resilient," Mr. Flaherty said. "At first she cried. Then she was more concerned about what this little girl looked like."

Much healing has taken place in the world of Shawn and Debbie Flaherty. Their marriage, close to crumbling 14 years ago, has been set aright. They have two more children -- a son, 10, and an 8-year-old daughter.

To the extent a visitor can gauge, it appears to be a happy family.

On the night I stopped by, the 16-year-old daughter was busying herself in the kitchen and glorying in a good report card.

The two younger ones -- a comically inseparable brother-sister combo -- were nibbling Chinese takeout and happily drawing pictures for each other. It is hard to imagine what it will be like when they find out.

But there's little question they will. Politics today respects no levels of pain and whatever tears come in the next few days will be shed out of sight.

It was Feb. 22 when Shawn Flaherty got the phone call at his Shadyside law office. A staffer for the Republican nominee in the April 11 special election in the 30^th House District in the northern suburbs had just seen the report the other side plans to spread. Someone, Mr. Flaherty surmised, had seen his family court file.

"He wanted me to know that he felt horrible," Mr. Flaherty said. Shawn Flaherty grew up in politics. His father was Pete Flaherty, the legendary Pittsburgh mayor and candidate for governor and U.S. Senate.

"Things were different then," he said.

Now he's waiting for the hammer to drop. That it will land on his family as well as him is, I suppose, one of the details of a political strategy in which it is less desirable to defeat candidates than to frighten them away.

Mr. Flaherty and his wife talked it over. He suggested he drop out of the race. She told him to stay.

"It's just shocking that I even have to be here talking about it. I'm shocked that I have to be confronted with this," Mrs. Flaherty said. "The way I look at it, there's one more healthy, happy child out there."

Healthy and happy: With luck, Shawn and Debbie Flaherty can provide the former for their children. That latter, for the short term, seems a bit problematic because of what politics has become.

Any man not too full of himself to admit the truth knows he could, under the wrong circumstances, find himself in Shawn Flaherty's position. Perhaps it is not a child out of wedlock. Maybe it's a drunken driving arrest. Perchance, having once been young, he experimented with drugs. Could be an intemperate remark, or a discredited political opinion, or an offhand remark to which the fairest response is a question: "What do you mean by that?"

The Flaherty family has long known of Shawn's problem. Sometimes knowing about a problem long enough makes it less a problem than a painful detail of history that, while not forgotten, can be overcome. He and his wife did precisely that, as did the mother of the unnamed child. The little girl was adopted young enough that she might well not remember; she might know nothing of her history. The Flahertys' 16-year-old daughter was 4 when the baby was adopted and doesn't remember the times her parents took her on visits with her sister.

Sometimes memory heals. Sometimes forgetting can do the same.

Forgetting ceased to be an option one week ago.

When he learned about the opposition research report, Mr. Flaherty decided to stay in the race and to acknowledge the single, worst thing that anybody can know about him. In the course of an hour's interview, he was asked about names, dates, child support payments and nothing about the state budget, property tax reform, casino gambling, workers' compensation law or any of the other things legislators actually do that matters to the electorate. In short, we have no idea what kind of legislator Shawn Flaherty would be.

How we judge him as a man depends on whether a man is measured by his mistakes or his willingness to admit them.