I never cease to marvel about the incapacity of (apparently) all/most frontline politicians to appreciate the power of such self-constraint. I call it "being caught in your own web of lies".
Because if you ground your policies on reality, and explain such grounding, when the situation changes, *you can* change policy without looking like an unelectable fool.
But when you have to also defend *previous lies*, THEN your options get seriously constrained.
How much your past lies constrain your future options is a function of your own image and rhetoric.
If your biggest assets are your perceived honesty and straight-talking, the effect is stronger.
That's a problem, especially because #Labour members and potential voters are self-selected amongst those who do pay attention (2nd mechanism).
This strategy, to my surprise, it is not already guaranteed to fail, but it certainly is one other thing: desperate.
Take home msg: if your opponent lies often and with profit, it DOES NOT MEAN that you can do the same. Quite the opposite, in fact.