Wigley's 'gaffe', Healey's law and shooting messengers
It's known as "Healey's law" or "the first law of holes". When you're in a hole, stop digging.
It's usually sound advice for politicians, although the transcript of yesterday's BBC interview with Lord Wigley suggests even experienced political operators sometimes forget a law popularised by the former Labour Chancellor Denis Healey.
Lord Wigley had made the comparison with Auschwitz off-the-record before the audio recorder was switched on. He then chose to introduce it during the recorded interview and when challenged - offered a way out, some might say - by Ross Hawkins chose to continue while trying to make his point that the nature of work has to be considered and not just that a job exists.
It's fair to say Lord Wigley is respected and liked across parties. Many of his opponents reacted more in sorrow than anger. Some were shocked but there was a general reluctance to put the boot in.
Conservative former Welsh Secretary David Jones said Lord Wigley was "a gentleman" but added: "His remarks were crass and bound to cause offence. While the apology is a bit mealy-mouthed, at least it is good that he has acknowledged they are offensive." (The apology was swift - 45 minutes after his comments were broadcast - but a qualified one, apologising for offence caused)
The (Liberal Democrat) Scottish Secretary Alistair Carmichael said the comments were offensive to both Jewish people and workers at the Faslane base.
The comments didn't go down well with Plaid Cymru's SNP partners either. First Minister Nicola Sturgeon said: "I'm certainly against the extension and replacement of the Trident nuclear system but I wouldn't have used the language that Dafydd Wigley has used and I do understand that he's apologised for any offence he's caused.
"It's not how I would choose to express the argument. My argument is very simple at a time of austerity when you have Labour and the Tories coming together to vote for £30bn of additional cuts the last thing we should be doing is spending a £100bn on new nuclear weapons."
Besides Healey's law, there's another rule worth observing in politics: don't shoot the messenger. Lord Wigley told the Daily Post the BBC had reported his comments in a "totally wrong" way. You can read the transcript and judge for yourself.
Presumably he feels similarly about all the other news organisations - among them the Press Association, Daily Telegraph, The Times, The Scotsman, the Western Mail, the Daily Mail and The Herald that have covered the story.
After four decades in politics, Lord Wigley - Plaid Cymru's general election co-ordinator - has a lot of goodwill in the bank, enough for opponents to give him the benefit of any doubt. But if a prominent figure in a UK-wide party had used similar language I suspect they would be out of a frontline job faster than you can tweet "Emily Thornberry".