Over the next two weeks Mr Corbyn can determine the fate of Mrs May’s EU Agreement. If he placed a three line whip on Labour MPs to vote for the legislation necessary to bind the UK into this new Treaty, he would give Mrs May enough votes to secure the matter. There might well be more Conservative rebels against such legislation, but not enough to prevent a grand coalition of Mr Corbyn and his loyalists with Mrs May and her government appointees putting through the necessary law. So far Mr Corbyn has been unwilling to do this, even though Labour has not made much of a case against the terms of the so called Withdrawal Agreement. We saw the kind of votes we could expect in such circumstances on the vote about the latest delay to our exit. Delay won by 400 to 120, with only 133 Conservatives voting for the delay despite a three line whip to do so.
Instead Mr Corbyn has concentrated on criticising the attached Political declaration. Understandably he has argued that signing the Withdrawal terms does not place the UK in a good position to secure the kind of eventual exit from the EU that he and others would like. He has placed considerable emphasis on his wish to see the UK stay in a customs union with the EU, though he has also hinted that he would still like some independent trade policy. It is difficult to see how these two usually incompatible positions could be negotiated with the EU. He has also made it official Labour policy in certain circumstances to have a second referendum to endorse any Agreement, though he seems more flexible about this than the Blairite wing of his followers.
Mr Corbyn now has to recognise that Mrs May could end up conceding the customs union. If she has her way and puts indicative votes to the Commons again, the customs union proposal without a Conservative whip on to oppose might get through. It has been voted down several times before because it was Conservative policy in the last election to oppose it, and because 3 line whips were placed against it. It would only take a handful of Conservative rebels against the Manifesto to tip over the vote, assuming all opposition parties coalesced around the proposal. Mrs May would probably then change her own mind and recommend the customs union.
This could place Mr Corbyn in a more difficult position. Why would he wish to take responsibility for the Withdrawal Treaty and for rescuing Mrs May’s government? Why would he hand her a big win, finally vindicating her tenacious support for a Treaty which is opposed by a big majority of the public? More Labour than Conservatives might end up voting for the legislation it needed. He still has a couple more options. He can argue that he dislikes other features of the proposal as well as the absence of the customs union to avoid commitment. He could help her win the first vote but then find detail in the legislation he could not support, creating subsequent chaos amidst allegations of bad faith.
The way out appeared to be to rewrite the Political declaration, as the EU used to say there was some flexibility about that document. That seems to be closed off by the tough terms of the recent extension, where they categorically rule out any further discussions of the future partnership until the Withdrawal Treaty is adopted in UK law.
Mr Corbyn’s safest course is to find another reason why he cannot bring himself to back this Treaty, He has been talking about worries over who the next leader of the Conservatives might be, what kind of future partnership the Conservatives would want to negotiate, what trade deals they might do elsewhere and other related matters. He could even start to expose some of the undesirable features of the Agreement. Were he to give the government support not just for the first vote but to get through a very contentious and important piece of constitutional legislation to enforce the new Treaty he might unleash uncontrollable forces amongst his own voters and members.The curse of the Agreement might gravely damage his party. This is a draft Treaty which unites many Leave and Remain voters in opposition to it. Labour MPs in Leave voting seats would be particularly uncomfortable, whilst the left would make unusual supporters of Mrs May.
The worst outcone for Labour would be securing a second referendum. The party would then become a pro Remain party and lose most of its Leave voters. It would be scorned by at least half the electorate as anti democratic for going back on its word to accept the result of the original referendum. It would need to defend its new found enthusiasm for all things EU including its austerity economics.