I've wondered this for a while, but Daily Howler said it better than I could:
It’s time for a Missing Person Alert: Whatever happened to Candidate Bush, the fellow who ran for office in Campaign 2000? As a candidate, Bush endlessly swore that a $1.3 trillion tax cut was all we could possibly afford [I think he said $1.6 trillion - John]. More than that, the candidate said, and we’d have to start spending the Social Security surplus—something he just wouldn’t do. As a candidate, Bush swore that he’d take all future SS surpluses and use them for Social Security.
But that was then, and this is plunder. To all appearances, Candidate Bush has been replaced by a slick and dishonest impostor.
There's more and all of it good (it begins here and continues here).
The actual numbers get pretty mind-boggling: $1.25 trillion in 2001, some minor additions in 2002, another $350 billion this week, and they’re already ramping up for the next round. Add to this the fact that his original numbers were based on the optimistic surplus estimates at the peak of the boom, we’ve gone into a seemingly endless recession, the military budget is ballooning without limit, we have two wars (so far) to pay for, and the numbers for each cut were cooked to look much smaller than their real cost. If the big pie could only afford $1.6 trillion, how can the smaller pie afford over $3 trillion?
There is a simple explanation to the mystery of the unending tax cuts: the Republicans want to bankrupt the government. When stated that baldly, it sounds like a conspiracy theory or opposition hyperbole. It is neither; this has been a stated goal of certain parts of the Reagan right for twenty years now. For years Republican strategist Grover Norquist's best laugh line has been how he wants to cut government "down to the size where we can drown it in the bathtub."
It's an easy and ugly strategy: rather than taking the politically dangerous action of curtailing popular programs, simply make the federal government unable to pay for them. After that a number of mechanisms finish off the programs. They can close them down with an insincere apology, “we’d love to keep it, but we can’t afford to.” They can cripple them by making oh-so-fair-looking across the board cuts. Large or well-funded programs can afford a ten percent cut better than little or over-worked programs. They can shift responsibility to the states.
This last strategy may backfire. Back in Reagan’s day Democrats controlled two-thirds of the state houses. This meant federal Republicans could make programs untenable and make state Democrats do the politically difficult work of either ending them or raising taxes to pay for them. Look at the situation of the states today; most would rather cut programs than raise taxes. However, Republicans now run the majority of the statehouses. The Republicans at the center are screwing the Republicans in the states. Wasn’t it an arrangement like that that caused the Democrats to loose the solid South for a generation?