One interesting aspect is from the election when Bush wanted to spend a lot of the surplus, and the line then was that it was affordable, that there would be enough money left. So at that stage even he didn't believe that that tax cut would stimulate the economy so much that it would repay itself with interest. What he should have said then was with his tax cut they would end up with an even bigger surplus than before.
Then the recession occured and all of a sudden the same tax cut was suppose to pay for itself and reduce the deficit. They didn't believe that themselves at the election though. They know themselves supply side economics doesn't work, they only dredged it up again so they could get enough cuts through to pay off their contributors.