If the polls and the buzz are right then Jeremy Corbyn is about to become the leader of the Labour Party. He has fought an energetic campaign, and has clearly enthused some people unmoved by his rivals. He has also tapped in to anxieties and anger about New Labour, Ed Miliband's failure to defeat David Cameron, and a desire to see an end to austerity.
But if he wins there then comes for me a far bigger question: can he win a general election? And on that I fear the answer is no.
Having spent most of my adult life trying to help get Labour into power and keep the Tories out, I think those being swept along by Corbynmania need to be very careful in what they wish for. They like to claim a monopoly of principle for their man against three others they deride, unfairly, as mediocre careerists.
Principles are essential in politics, as in life. But to put those principles into practice in a way that makes Britain a better country – as the all too few Labour governments have done – you do need power. I do not believe, no matter how popular he may be in the Labour Party right now, that Corbyn can achieve that.
So here are five reasons why I advocate ABC: Anyone But Corbyn.
1. He cannot win a general election
The Labour Party may elect Corbyn but, I believe, the country will not. A country that decided to reject Gordon Brown, Neil Kinnock, Ed Miliband and Michael Foot is unlikely to elect someone to the left of all of them.
Ken Livingstone has said that anyone could have led Labour to win in 1997. Not so. We won those three elections because we had a leader who understood not only political activists but the lives of those who did not exist inside a politically obsessed bubble, and we had practical policies to meet the challenges of the time.
And we did not lose the last election because we were not left-wing enough. We lost because people did not see Ed as a Prime Minister, because we had lost trust on the economy, and because we spectacularly failed to rebut the idea that Labour caused the financial crash.
2. He will unleash chaos in the party
Corbyn will not be able to unite the party around his vision and policies. He is someone for whom rebellion is in his DNA. Politics needs people like that, but with 500-plus rebellions to his name, Corbyn will not be well placed to inspire or call on the kind of discipline that all leaders need to rely on to gain support for often difficult decisions.
I do not believe the party will split but he will find it very hard to hold the PLP together. There will also open up a huge gulf between members in the country and the PLP, and amid the chaos Corbynmania will evaporate even more quickly than Cleggmania before it. The charge of betrayal his supporters have for years laid against Labour leaders will come very quickly on him once they realise the words at the mass rallies are they easy bit.
3. He lacks policy-making experience
Corbyn has never done the hard graft of detailed policy making. Standing up and saying you are against something that another leader has put forward - and Jeremy has decades of experience of that - is a lot easier than putting forward the detailed policy prospectus required of a serious opposition party.
We all want the greater equality, opportunity, social mobility and fairness he wins applause for. We all want to fight poverty home and abroad - and I would argue the last Labour government did plenty of all that. The slogans are easy. Policy making that wins broad support and stands up to real scrutiny is something altogether different. I am not convinced he can do it.
4. His supporters will hold Labour back
Corbyn himself is a nice guy, but I am not so sure about some of his friends. There is a real cybernat feel to some of his supporters and their zealous belief that even to suggest he is not the man to lead us back into power is a form of treason.
It is great that he is enthusing young people and drawing big crowds to his meetings. But among his biggest backers are people and organisations who have always seen control of Labour as being of much more importance than Labour winning power – even if it means increasing the chances of a Tory government. I have no idea if the claims of mass entryism are true, but I do believe that even if he wants to be an inclusive leader his backers won't allow him to be.
5. His foreign policy is a minefield
His stated positions will come under massive scrutiny and won't stand up to it. Just take one example: withdrawal from NATO. This has passed virtually unnoticed. If Corbyn is elected leader and tries to make withdrawal party policy, that alone, in my view, could lose an election. His career has laid a minefield of silly positions and bizarre alliances that will come under huge scrutiny.
The Tories are a ruthless fighting machine, already storing up the ammunition. That, and the media campaign alongside it, are not in themselves reasons to oppose Corbyn. But the positions he takes that attract so much criticism are, and the Labour party needs to know what it is letting itself in for. It is possible to be a nice guy, but also wrong about a lot of important issues.