I'll start, and then perhaps my colleague may want to add some points as well.
We do challenge when new policy measures are being introduced and have gone through cabinet but come to the Treasury Board. We scrutinize those measures on a couple of bases: one, that they're consistent with our policies, whether that's a procurement policy or any number of Treasury Board policies; and also, that the funding that's being requested is appropriate for that particular policy initiative. We need to check often with the Department of Finance to ensure that the funding is in place, that there is a source of funds for the initiative. We put a fair amount of due diligence into all of these issues as they come before Treasury Board.
Subsequently, and even after they have become part of a department's reference level and they are ongoing, we provide continuing scrutiny; we are continually looking at whether in fact programs are effective, whether there's value for money in them. We require departments to establish performance measures for the programs. We ask them to report on performance. So we ask not just in their planning documents but also in their performance reports to tell us how the programs are working. Then we scrutinize them even more thoroughly and in great depth through strategic reviews.
Those are some of the ways in which we exercise a challenge function. Maybe my colleague might have other comments.