Update: See this follow-up post, which corrects some mistakes made below. I've added comments pointing out which parts needed revision.
In the early years of the millenium, the federal government ran what appeared to be an indestructible series of budgetary surpluses. No matter how many tax cuts were implemented, it ended each year with a sum of money so large that its biggest fiscal policy challenge was to find legal ways to spend it.
Those days are over, of course. Dealing with the deficit will - or should - be a theme of the upcoming federal budget. So it's worth spending some time thinking about just how the policy decisions of the current and previous governments managed the trick of transforming that indestructible surplus into what looks to be a stubbornly persistent defict.