The combined difference turned out to be $1.8 trillion.
But, you might respond, those estimates were published a month before the attack on September 11th, 2001, so of course they turned out to be way off!
And that’s my point. With the exception of Keynesian economists, no one can predict the future. All it will take is another major terrorist attack or another war and it’s adios spending caps. I would argue that such unfortunate scenarios are a distinct possibility given the Beltway crowd’s love for empire, but I’ll leave that topic to Cato’s foreign policy experts.