Not that Cameron is invulnerable on Libya, anything but. Luckily for the PM, the Leader of the Opposition gave it a knockabout treatment and got knocked about in return – and so hard we could hear his enormous teeth rattle.
The first wallop was a response from the PM to the charges of making a complete foreign policy Horlicks of it all. Failed flights, seized soldiers, and internet rumours broadcast by the Foreign Office. Cameron said he'd take no lectures from the party of Gaddafi and Megrahi.
It's not a complete answer when you read it in cold print, is it? It doesn't exactly go into the machinery of risk assessment and operational decision-making. But you at home can't hear Ed Miliband's teeth rattling (they sounded like castanets).
The second wallop followed Miliband's reference to Cameron's "deafening silence about the performance of the Foreign Secretary". Cameron fixed him with that glittering Etonian eye that takes pleasure in careful cruelty. He said: "Only one person round here has knifed a Foreign Secretary – and I think I'm looking at him."
It was then Ed made a career error. He said that the more Cameron referred to his relatives, the less he had of the argument. "I have a second cousin in Belgium he will be going after next."
The Labour Party really picked up then. Another Miliband! Yes, in Belgium but maybe he could speak some sort of English-sounding Walloon? Did he have leadership qualities? Can a person born overseas be Prime Minister? More easily than Ed, you could see them thinking.
Ed just sat there with a little Zen smile. He can certainly handle ridicule and abuse, he just soaks it up. Years of training under Gordon Brown.
David Winnick asked a serious question and got a serious answer. Would the PM "guarantee" that no action would be taken without a Security Council resolution? The PM said that he and President Obama were planning for every eventuality and that everyone wanted the widest possible backing and there was a Security Council resolution being drafted and that was the right thing to do.
Or more succinctly: no. No, he wouldn't guarantee action would be authorised by the UN.
Is that significant? Or is it something a prime minister can't say in public? Does he have to keep his cards hidden from our opponents – the French, for instance?
It did just sound a little too like Tony Blair than Labour – or indeed the Tories – would like.
PS: Essential advice to Ed Miliband's brand builders. When you want to deride a prime minister for incompetence you absolutely have to have a more conventional haircut. Why? I don't make the laws, I just report on them.