The annual net interest payments on the Federal debt is $255 billion. Since the Government receipts are over $3,000 billion per year, there is no chance of any default on US debt obligations. That tax revenue works out to be about $250 billion of tax revenue per month and interest payments are about $20 billion per month. All entitlement spending is another $125 billion per month. That's $145 billion of absolutely essential spending per month versus $250 billion revenue. So all Medicare and Social Security checks can go out. All interest payments can be made---easily.
Yes, the interest payments (and tax collections) are "lumpy" meaning there possibly needs to be a cushion of money in the coffers. To do that, we should have started the debt negotiations several months ago rather than days ago. Or, the President needs to sit down and talk to the representatives of half of the population of this country---that half of the population that doesn't want unrestrained growth of debt.
This fear-mongering on the part of the Treasury (Jack Lew) and Obama is unbelievably irresponsible. Rather than encourage the markets and re-iterate that there is no circumstances that the US would default on any of the debt, they are literally trying to scare the markets. Just how is that statesmanship?