BBC News Online political correspondent Nick Assinder gives his instant verdict on prime minister's question time from the House of Commons.
Iain Duncan Smith has finally found his sound bite.
"Nobody believes a word the prime minister says."
He actually put it more bluntly during question time when he accused Tony Blair of lying, as usual.
But it is the sound bite that will do the damage and that will be repeated time and again between now and the next general election.
You can already see the election posters with the slogan: "How can you tell when he's lying - because his lips are moving" over a picture of the prime minister .
The trouble for Tony Blair is that it is not just the leader of the opposition who is saying it.
Two former ministers - Robin Cook and Clare Short - are saying it in public, and many backbenchers are saying it in private.
Even more will candidly admit that, given the government's record of spin, dodgy documents and the like, it is mud that may well stick.
And by the look on the faces of those on the Labour frontbench, it has dawned on them that this is a pretty effective weapon.
It will damage politics more widely, because it plays to the public perception that "you can't trust any of them."
But, as sleaze helped do for the last Tory government, this may just help do for New Labour.
The prime minister tries to laugh it all off, but it's pretty hollow laughter.
And his own MPs are no longer in any mood for levity.
That was abundantly clear when he expressed surprise that Iain Duncan Smith had attacked him for implementing a Tory manifesto pledge.
Just how funny did he think his own MPs would find the idea of him pursuing a Tory agenda?
Bernard Manning would have got more laughs at a synagogue.