I wouldn't really call his past decisions insane, although I agree with you that he's our (German) version of a political hardliner.

Personally, I would describe his reasoning and actions as in line with the aim of always putting the German state (not necessarily its people) first. Maybe his idol is Bismarck, maybe there's some other reason for his actions. Who knows; I surely don't. It is possible, of course, that his views and behaviour have become quite disconnected from the "real" world. After all, he's been a MP for 43 years now - making him the most senior MP in the history of the FRG. But then, he's seen quite a few global disasters happening from a political perspective.

In the end, right now, he's doing a fairly good job of maintaining a stable German economic position in the EU/the world and is able to even strengthen Germany's global political position as well. This rather aggressive damage control certainly doesn't support the ideals that the EU is built upon, but then who knows whether he subscribed to it in the first place? I honestly believe that, should the EU fail in the coming decade, he'll be remembered quite positively.

I can kind of see how the first two could maybe, possibly, be seen as not insane. However, how do you defend the Bundestrojaner thing, in light of the fact that what he intended was literally impossible?

I would call that a profound lack of knowledge (or concious ignorance thereof?) in combination with the fact that it's always better to claim the impossible (because you can polarise the masses more easily and scale down your claim later on once the main challenge - getting things things passed - is done with).