I don't think he paded his CV too much. Telford, the de facto most powerful woman in Canada, says it herself at the beginning of this video how much of a big shot he was.
link to video
Considering how powerful Telford became, and now is, it's an interesting statement. But you are right, maybe he realized he wasn't going to have much power, so that's why he sent the letter so early saying he would have influence. He realized he wouldn't. so better before the end of the campaign. Which still begs the question: Who pushed this out to the press? I don't believe the Liberals, even the lefties, would jeopardize their own campaign like that. Maybe they wanted it to come out just after the election, and some reporter got the scoop early? Still so many questions with this affair not answered.
On the other hand, I think the beginning of your post is on to something. He was going to be squeezed out, so with the letter being leaked, he felt useless and used, and now he couldn't even use the last two years of his life - that would help him so much - on his CV. But to try to take down something that he had worked on for so long, instead of just being quiet and doing the "politically correct" thing and being a good soldier,, he must have been so angry he just exploded.
Maybe he felt like a cuckhold leader with Telford there, and had had enough?