But that's not enough. Because voting down the withdrawal agreement leads to us leaving with No-Deal, if nothing else happens between now and March.
So if May sits there saying "It's my deal or no deal", and we reach January/February with no other movement, frankly MPs are going to need to vote for the deal, to avoid no-deal. Which, no matter how much I hate Brexit, would be far far worse that the Withdrawal Agreement.
And I doubt very much that we're going to get a simple "Cancel Brexit". Politicians are far too nervous about "The Will Of The People" to do so without another referendum.
Getting that referendum is going to require one of three things:
1) An amendment to the Withdrawal Agreement vote which says "Only once a referendum has confirmed it".
2) Replacing Theresa May as PM with a Conservative PM who wants a referendum.
3) Replacing Theresa May as PM with a non-Conservative PM who wants a referendum.
I'm not sure there is an option for (2) who stands any chance of election as leader of the Conservative Party. Happy to be corrected there.
(1) and (3) require Labour to vote for it. The good news is that every Labour constituency now wants a second referendum. The bad news is that Labour's leader is against a second referendum. And that there have been mutterings from Labour about trying to renegotiate the deal if it gains power. Which, frankly, isn't going to get anywhere. The EU isn't going to make a better deal than the one it's offered (which is already better than I thought the UK would get). There's a good update hereon the European view of where we currently stand.
So the question, at the moment, is how Labour are going to act. How much the party leadership can sway the MPs. So, if you have a Labour MP I recommend letting them know how much you want a second referendum, and how much any backing you might give them in the future depends on it.
Both options also require sufficient Conservatives to vote for them (or, at least, not vote against them). And the Brexiteer wing definitely don't want a new referendum. So if you have a Conservative MP and you think there's any chance that they are either willing to vote for a second referendum off their own bat, or are in a marginal seat, then talk to them too. (All Conservative marginals _also_ want a second referendum). (The chances of Conservative MPs bringing down the government is pretty low. Although a sufficiently unpleasant Brexiteer determined to bring about No-Deal might be enough to make some of them finally show some backbone.)
Anything I've missed there?
Original post on Dreamwidth - there are comments there.