The second followed from the first: the 2010 show made it virtually impossible for Cameron and his successors to stand aloof without being called “chicken”.
I doubt whether the first mistake did him or the nation much harm, even though he ended up in coalition with Nick Clegg who was judged the winner of the tripartite debate of 2010.
Nor will anybody be able to prove that last week’s event damaged him, the Tories or Britain, even though the Scottish Nationalist spendthrift nation-wrecker, Nicola Sturgeon, was hailed the winner.
So, why do I bother claiming that Cameron has made two election mistakes?
The answer is very simple: up to 2010 televised debates had not been seen as an election forum. Margaret Thatcher stuck to that line while acknowledging that successive Prime Ministers had felt they had more to lose than gain from them.
But there are more substantial reasons for giving them a wide berth. To start with, the fate of the nation should not rest on whether a party leader is photogenic.
Before TV tightened its grip on the body politic, the skeletal Sir Alec Douglas-Home reached No 10 but later the now deceased Robin Cook didn’t. The jury is out on Ed Miliband.
Second, the nation’s governance is too important to swing on a soundbite. That is really all that TV affords in steadily reducing the public’s attention span to approximately five seconds. I’ll bet most viewers’ minds wandered during each of the seven one-minute pitches allowed last week’s contestants.
Third, the very nature of television – lights, action, moving pictures – distracts attention from the words being spoken. Radio is vastly superior at conveying ideas, though television began promisingly with those long and educative John Freeman interviews.
Now I sometimes think TV producers will not be content until they can feed the couch potatoes with a diet of soft “celebrity” porn set to rap “music” and seen through a swirl of reefer smoke. They go for the lowest common denominator.
The only amazing thing is that they think TV debates are worth prime-time viewing.
They are, not because of the broadcasters’ concept of public service, but because they might produce something more dramatic than a heckler who has – as last week – to be slung out of the studio because she is wrecking the timetable.
The fourth reason for giving TV debates a miss is that they are artificial – a contrivance of impresarios, not debaters. They most certainly will never tell you who would make a better Prime Minister than the incumbent because nobody can know until they are doing the job. By that time it can be too late.
Finally, government is far too complex to leave TV to identify the apparent answer to the nation’s prayer. Of course, personality counts in a Prime Minister but what matters more is his policy. And that needs to be consistently explained to the nation over the course of a Parliament.
I had the advantage over successor No. 10 press secretaries in that TV offered at least three hour-long “blockbuster” interviews over the year with Sir Robin Day, Sheffield-born Sir Alastair Burnet and Brian Walden.
They were arranged well in advance and sometimes came at inconvenient times, such as the troubles with Nigel Lawson. But Thatcher went ahead with them to explain under tough questioning what the government stood for and how it was making progress. There wasn’t much for six years.
In between, she sought to till the soil of public understanding through many other interviews, briefings and on the floor of the Commons. Steady, patient exposition over time is what matters.
Last week’s “debate” told us nothing we had not gleaned before. The Scottish and Welsh Nationalists can’t wait to get their hands on more English money. Together with the Greens, they would break up the UK. And, together with Labour, they would wreck the economy with their spending.
Nigel Farage is the hornet in the Establishment’s nest, hoping that the electoral arithmetic will give him the chance to use his sting. And Nick Clegg wants to moderate either a Tory or Labour-led coalition and so again slow down Cameron’s economic recovery in the name of “fairness”.
All TV “debates” are little more than a gameshow. That is why Cameron has compounded Brown’s original mistake. They dumb down politics when the art needs uplifting.