Can't tell if you're joking, but I think they mean that the positive effects of making the promise are immediate for Macron, but he won't have to deal with the actual cost, logistics, political maneuvering, etc., until after he's re-elected, if at all. Cynically, he could make promises he has no intention of keeping.

It goes both way, isn’t it? Whoever in power in 2035 who will get to cut the ribbon of the reactors will make it like their own victory. Macron’s name and whatever he would do to make it happen will be conveniently forgotten.

It's a pity that we should be completely carbon neutral around 2040 give or take a couple of years and power plants that go online in ten to fifteen years (if they are actually done by that time) save zero emissions until then.