I think we're have some fundamentally different assumptions about the process here: I know that tax revenues in this month are more than enough to pay off the interest due on the national debt this month.
But T-Bills come with maturity dates-- that means not only the interest but the principal is also due that month, and that (I think) is where the problem lies-- if we can't borrow more money to pay off the principal on the notes due when they are due the we are in default.
Now, that doesn't particularly bother me, because most of the 6 trillion borrowed in Obama's term went to his political supporters and through the Fed to the Wall Street banksters. So I don't see why I'm obligated to pay back money borrowed in my name as part of a fraudulent conveyance.
Its called float. Ever send out a check before the paycheck comes in? Businesses, individuals and governments do it.