Before this week, no screenwriter would have dared cast the former senator Pete Domenici, the very embodiment of family-values rectitude, in a steamy soap opera on Capitol Hill in which he sires a love-child with the 24-year-old daughter a Senate colleague. Even in scandal-weary Washington it wouldn’t have been believable.

Mr Domenici, a Republican who was the longest-serving senator in New Mexico’s history when he retired four years ago, was among those who tried to get President Bill Clinton impeached in 1999 for his liaisons with Monica Lewinsky (though in a speech to the Senate he said it wasn’t the sex bit that bothered him but the fact that Mr Clinton had lied about it).

That speech – in fact the entire career of Mr Domenici – will be viewed in a new light since his admission this week that he had an affair in the 1970s with a 24-year-old woman called Michelle Laxalt. She happens to be the daughter of the former Nevada senator and governor Paul Laxalt, a close friend of Ronald Reagan and a hero of the conservative right. And they had a son, Adam – now 34 and a lawyer in Las Vegas – whom we are only now learning about.

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After decades of silence Mr Domenici and Ms Laxalt sent statements to an Albuquerque newspaper owning up to everything out of fear that their secret was about to be spilled by a national tabloid.

Mr Domenici, who is 80 and has fathered eight children with his wife of more than 50 years, Nancy, said in his statement that he “deeply regretted” his behaviour. Ms Laxalt, a powerful lobbyist and pundit in Washington, said Adam was conceived after “one night’s mistake”.

Adam himself has told The Washington Post he wants nothing more do with the scandal.