The national deficit is created by a simple equation. Money spent - taxes collected = deficit. Note how there are two sides to the equation, spending and taxes and how they have an equal impact on the deficit? I.E. if you increase spending by a billion dollars it has the exact same impact on the deficit that cutting taxes by a billion dollars does.
The GOP want to pretend that taxes don't affect the deficit, that spending is the only part of the equation. Here's Sen. Jon Kyl, the other Republican from Arizona, claiming that you should never have to offset the cost of a tax cut, as if that's some kind of accounting rule.
A tax cut adds to the debt. Bush's tax cuts to the wealthy will cost $678 billion just as sure as spending $678 billion on tanks, or health care or free pie for everyone in America. Tax cuts raise the deficit.