Nick Robinson: What is it PM 'gets'?
"I get it" says the Prime Minister - but what exactly is it that he gets ?
First, that British public and parliamentary opinion simply does not have the stomach for another military intervention.
For months at home and abroad he has made the case that Syria risked not being another Iraq but another Bosnia - in other words a war that the West should be ashamed for not intervening in.
In theory he could have tried again even after last night's defeat but instead he's concluded that Parliament has given its final verdict on the issue.
He knows that defeat in a motion specifically authorising military action - which last night's did not - could be politically terminal, as against merely humiliating and wounding.
What Mr Cameron also gets is that there is now a significant section of his party so independent or so irreconcilable that they will vote against him whatever the consequences.
What's more, he understands - if he didn't before - that his opponent Ed Miliband can be politically ruthless.
What troubles the Prime Minister and those around him more, though, is the question of whether Britain has lost the appetite to be America's most reliable ally. The thought of America attacking Syria with French and not British support pains them.
George Osborne says it's time for some national soul searching. That's already begun inside Downing Street.