The remarks were recorded in sinister circumstances, but now they have been revealed he cannot with any stature remain as Business Secretary. A decent, informed, radical politician has to pay the price not just of indiscretion but poor judgment.
How would any senior business figure from now on feel if they were involved in negotiation with Mr Cable? What are his Cabinet colleagues of whatever political colour to make of him from now on?
His insights on banking reform, the financing of higher education, the promotion of more competition in the economy will now be treated with polite but real derision. His identification with economic expertise and reforming zeal has been ruptured.
Coalition politics should rightly be seen as a political experiment. It has been set back at least six months by this fracas.
A new Liberal Democrat Cabinet member should be appointed to the post as soon as possible. Hopefully he or she will recognise the real responsibilities of Cabinet.
What The Daily Telegraph undercover reporters did was unpleasant but not illegal. MPs' constituency surgeries will be more tense affairs from now on. But the lesson to be learned is that coalition government and Cabinet membership needs a mindset which many of Mr Clegg's party have yet to grasp.
Is it any wonder that The Daily Telegraph targeted LibDem ministers in an attempt to get them to say something unwise in an unguarded moment?
The truth is that certain sections of the Tory-supporting press have been very unhappy about the whole coalition idea right from the start and would be delighted to see it sink without trace.
Is there any chance that they will try to catch out Conservative ministers and backbenchers saying what they really think about their LibDem colleagues? Maybe, but I doubt it - unless it helps to break the coalition altogether.