Here is the US budget for this year.
http://www.gpoaccess.gov/usbudget/fy12/pdf/BUDGET-2012-BUD.pdf
Total expected spending: $3.8 trillion.
Total expected tax revenue: $2.2 trillion.
Deficit: $1.6 trillion.
If the government cannot issue any more debt, and we're not going to raise taxes, then the deficit must be eliminated by drastic spending cuts.
Interest payments are expected to be $200 billion. Those must be met, unless we are planning to default. Thus, we can only spend $2 trillion. Here are the line items of the budget.
Social security, $800 billion.
Medicare and medicaid, $800 billion.
Defense, $800 billion
Interest, $200 billion. (Can't cut that though.)
Everything else, $1.2 trillion.
As you can see, social security, medicare and medicaid, and defense account for $2.4 trillion in spending. That means if we eliminate "everything else," and I mean everything, we have to cut $400 billion from those three. What do you cut? Social security? Medicare and medicaid? Defense?
And remember, we don't have any government employees any more, because we fired them all, since they were part of "everything else," so no one will actually be collecting and disbursing any revenues from the government any more.
BTW, if we go cold turkey and are forced to match expenditures with revenues, i.e. not raise the debt ceiling, the government will stop spending $1.6 trillion a year, or about $130 billion a month, which accounts for 11.3% of GDP. IOW, GDP will start falling by about 1% a month. As a comparison, the economy fell by 3.1% top to bottom during this most recent recession. So forcing the government to balance its budget by not raising the debt ceiling would contract the economy in one quarter what it did during the entire recession.