If the manifesto is really that popular, then we will see the foretold stunning Labour victory tomorrow and neither of us will have anything to worry about.
But be warned: no victory tomorrow, and the very concept of left-wing politics will no longer exist.
To put it in your terms, captain, he's turned the ship around and only increased support since the introduction of the 'very left wing' manifesto. The obvious take away is to work more on that which has taken them to unexpectedly high support and less on what brought Labour down in the gutter. Your logic is non-existent. In other words: A better than expected (a few months ago) result tomorrow: MORE left-wing politics.