There is a cheap jibe that responds to the title of this piece by saying that Corbyn does not want to end Brexit. It is cheap because what Corbyn wants above all else is power. It is difficult to imagine this government surviving the collapse of Brexit, so ending Brexit is a means to that power.
Another idea that some Remainers have is that if only Corbyn had campaigned against Brexit from the moment the vote to stay in the EU was lost, the Labour party could have somehow swung enough public opinion such that support for Brexit would by now be collapsing, and the resultant pressure on Remain-at-heart Tories would be so great that they would have been prepared to bring down their government just to stop Brexit.
To see why this makes little sense start with the 2017 election. May wanted this campaign to be about Brexit. She would have wanted nothing more than Corbyn to oblige by supporting Remain. The reason is straightforward. The Brexit vote divided the electorate on social conservative/liberal lines, with social conservative (anti-immigration) Labour voters supporting Leave. May knew that in a general election right wing social liberals would return to the Conservative fold, but left wing social conservatives could have been persuaded to vote Conservative, or at least not vote for an anti-Brexit Labour party. As a result of all this, the only choice Corbyn had before the election was to triangulate over Brexit, and it is only because of this that May did not get her landslide.
The only possibility is therefore if Corbyn had campaigned for Remain from the moment Remain lost the vote, and that as a result he had been sufficiently stronger in the polls by the following spring to dissuade May from holding an election. This seems very improbable for two reasons. First, immediately after the poll many who voted Remain believed the referendum result should be respected. Second, the Brexit vote has stayed pretty firm despite a fall in real wages. Once you recognise that, Corbyn had no choice but to triangulate over Brexit. That may have been an easy choice for him to make, but it was also the wise political choice. Had he not done so, May would have got her landslide in 2017. If Owen Smith had become Labour leader he might have made an anti-Brexit campaign work, but that is now irrelevant speculation.
That is why wishing Corbyn had not triangulated is in effect wishing May had got her landslide. Triangulation is why Corbyn has endorsed staying part of a customs union (although he could have done so sooner). As one of the reasons Labour gave for doing that is to avoid any infrastructure on the Irish border they have effectively endorsed staying within the EU’s Single Market for goods: the so-called Jersey option.
But triangulation is a dangerous game, particularly if your core support is not clear that is what you are doing. You have to convince socially conservative Leave voting Labour supporters that you will respect the vote, but at the same time convince your Remain voting core supporters that you will always push for a softer Brexit and take any realistic chance you are given to stop Brexit.
That was why sacking Owen Smith was foolish. The general belief of most Remainers is that they only way Brexit can be stopped is a referendum on the final deal. Sacking Smith because he advocates this just weakens Labour’s support among Remainers for the forthcoming local elections. Maintaining shadow cabinet discipline gains him nothing, while appearing to cast aside the hopes of many loyal Labour party members is a big deal. You do not win votes by shattering dreams.
However Remainers also need to realise another important political fact. The remaining slim chance that Brexit can be stopped requires Corbyn to remain passive. The only people who can stop Brexit happening will be the handful of Conservative MPs that have in the past voted against May’s wishes. They need to support moves that initiate the circumstances that lead to a popular vote on the final deal. Those Conservative MPs will only support such moves if they come ‘from parliament’, and not if they come from Jeremy Corbyn directly. Anything that comes from Corbyn is too toxic, as George Eaton notes here. All that Corbyn can do is leave it to others to do what they can to facilitate that moment, and then go with it if it comes. And he will go with it, because it increases the chances that the government will fall.
Whether that moment will come depends not so much on Corbyn or Labour, but more on the EU. So far the EU have allowed May to pretend that there is another solution to the Irish border question than the Jersey option. They have even gone as far as to set out what any free trade agreement (FTA) between the UK and EU would look like. They must know that the only way that FTA could ever happen is if there was a border in the Irish Sea, and they must also know by now that this is politically impossible for May. To go down the FTA route when May will have to concede something like the Jersey option for the whole of the UK is a waste of their time.
The EU therefore has two options. It could force the issue, and make May choose between the DUP and Liam Fox, or it could allow her to continue to fudge the issue until after we leave in 2019. Remainers should stop using Corbyn as a punchbag for their frustrations as time runs out to stop Brexit, and focus that frustration where it may belong, which is in the EU’s apparent willingness to indulge May’s desire to keep her party together.
Here is why the EU should not allow this charade to continue. Brexit is and will always be a right wing fantasy project. It is an attempt by a small group of newspaper owners and politicians with Little Englander fantasies to persuade the country that by leaving the EU the UK could become more wealthy in economic terms and more powerful in political terms. In reality precisely the opposite is true. In order to keep the fantasy in tact the Brexiters have tried to vilify experts, take power from parliament and intimidate judges, and have called any dissent they face unpatriotic. In other words the attempt to make this fantasy work has required its opponents to threaten almost every aspect of our parliamentary democracy.
If such tactics are seen to be successful they will only be repeated elsewhere. It is therefore not in the EU’s interest to allow May to keep her party in one piece. Brexit has to be seen as a failure, just as it is essential that Trump is seen as a failure. That has to mean that the Brexiters lose what matters to them most: political power.  It is not in the EU’s interests to allow May to appease her Brexiters. The possibility that by not indulging May the EU risks a No Deal outcome is now non-existent.
One thing above all else Remainers need to see. Even if Brexit cannot be prevented in 2019, it is essential that those who masterminded it suffer for the harm they will inflict on the UK. The only way they will suffer is if they lose power, and Conservative party members come to see the Brexiters as the source of their subsequent misfortune. To imagine, as some Remainers seem to do, that this can come about in first past the post UK by some kind of centrist revolution is as mad a fantasy as Brexit itself.  Whether they like it or not, the Brexit project will only be seen as a political failure if it leaves its leaders hollow, and the Conservatives out of power for a decade, and that can only happen one way.
 The idea that Brexit needs to be seen to fail in economic terms with the Conservatives in power is misguided. Economic failure will be gradual, and as with Brexit itself the government will deflect economic problems by finding scapegoats that play well with social conservatives, and by ramping up nationalism. As Simon Tilford argues, Brexit poses a real threat to pluralistic democracy. This is the strategy that Republicans have followed in the US, and right wing governments in Hungary and Poland are also following with some success.
 If centrists are uncomfortable with what Labour has become, think instead about what the Conservatives will become once May finally goes. The top three favourites to succeed may are all Brexiters, and for a good reason.