In the long run congress will always spend a greater amount than what is coming in. The only way to slow spending is to slow tax income. Lowering tax income lowers the amount congress can borrow from the market which lowers the amount of debt the nation is able to carry.
An analogy is your personal budget. If your monthly income is reduced, you have to reduce the amount of debt payments you can carry. You will also reduce the amount of debt a bank is willing to loan. The same thing happens with governments. Their ability to borrow is directly related to tax income. The lower the tax income the lower the ultimate debt.
Ya know, this is my one worry about tax cuts. But I've never heard Democrats mention it in their opposition. I wonder why?