I have been told that this afternoon Defence Secretary Michael Fallon has been briefing Labour MPs alongside one of his top military aides, Lieutenant General Gordon Messenger, the Deputy Chief of the Defence Staff (Operations) who commanded British forces in Helmand.
Mr Fallon is also planning to brief Labour MPs collectively at an open meeting in a couple of weeks' time, followed by another briefing for Tory MPs.
And while Downing Street is still insisting that there is no guarantee there will be any vote over military action, that the prime minister will act only if he is absolutely certain of winning that vote, ministers believe the momentum is moving their way.
One Cabinet minister told me: "Yesterday was a game-changer. You could see the middle rank of Labour MPs, particularly the women, nodding along with the PM. Afterwards, he was bouncing. He really thinks the mood has changed."
And, having spent the morning talking to MPs at Westminster, that minister may be right. So what has changed?
As for the numbers, ministers reckon the 30 Conservative opponents of extending military action to Syria can be squeezed down to about 20. They are hopeful of similar numbers of Labour MPs backing them and even more abstaining.
The key aim for the Conservative whips is to try get enough mainstream Labour MPs onside for the government's policy rather than relying on old Blairites to stick it to Mr Corbyn.
Also crucial will be the role of the eight Democratic Unionist Party MPs.
Back in September, the DUP leader at Westminster Nigel Dodds firmly opposed military action in Syria.
But I note the way Mr Cameron praised Mr Dodds in the House of Commons yesterday and Tory ministers tell me they are hopeful of winning DUP support.
One DUP source said: "We wait and see: if the PM makes a credible case for what the use of British military force can realistically achieve, we could of course support that."
As one Cabinet minister told me: "There is now a confluence of events and stars in our favour. I think we can do this."
Maybe. But only if Downing Street is absolutely sure they will win.
David Cameron has yet to publish his new plan for extending military action to Syria but his team are already making the case in the House of Commons.