Tone is easy: a halfway decent speechwriter can do 'constructive'. But when it comes to actual content, it can't help falling into the classic Corbyn dilemma: he definitely wants out, but metro-Labour definitely doesn't. So he ends up with the feeblest of BRINO which (a) pisses everyone off; and (b) is the most blatant Trotskyite 'impossibilism'. And it faces the distinct possibility of lingering no more than 24 hours in the fast-moving news pages.
In that brief window, could it trip May, though? Here's how one intelligent, ever-hopeful lefty parses it, as optimistically as she can.
The case in favour of the five demands sees Theresa May’s chances of either replacing the backstop or securing a time-limit/unilateral withdrawal ability as non-existent. Corbyn’s letter quashes the notion that Labour wants to “frustrate” Brexit and applies further pressure on the government to implement a soft exit. This is the choice that the Prime Minister has faced since the start: leave with no deal and be responsible for chaos, or pivot to Labour’s plan. Both options seem unbelievable. Either way, the Tories split. That seems like a win-win ...As we've seen a hundred times, May can scarcely engage with anyone without trying to agree with them; so whenever she's been equipped with a nicely-crafted piece of 'constructive ambiguity', her next partisan interlocutor demands she clarify it in the direction they want it to be understood. And, ever-obedient to whomever is looking sternly at her at a given point in time, she complies (see her trip to NI for just the latest example). So for her strategy team, the whole 'Corbyn Plan' issue is simply to sound equally constructive for a day or so, and then let fresh weekend headlines take over. She's hardly going to supplicate, on the back of this, for the Art.50 delay that would be needed to negotiate it. (Is she ??)
So it shouldn't trouble the scorers at all, still less "split the Tories". As our Labour pundit is forced to conclude:
... but Corbyn’s proposal – which looks a lot like the unhappy compromise of ‘Norway Plus’ – does leave many on the left, from Lexiteers to People’s Vote campaigners, wondering ‘what’s the point?’.
Answer: it's the best he's got, to maintain a respectable profile whilst biding his time for the only real strategy he and McDonnell have ever had, viz letting chaos reign and have it squarely blamed on the wicked Tories. Part 2 of this plan, of course, it for them both to survive long enough to win the next GE. Can they hang around until 2022, though?