This week, Rishi Sunak just announced pushing back of a few net zero targets - but much more significantly signalled a shift in campaign positioning that has thrust the issue to the centre of the conflict between the two main parties in advance of the general election. Labour leader Keir Starmer now has to work out if this is a great opportunity, or a poison-laden trap. It's a more subtle question than the ideologues on either side think it is.