美国债务上限难题：先还债，还是先发社保

    这可是个大问题，原因是政府每个月都必须用新债券来代替到期债券，或者说实现“转滚”，否则政府的债务负担就可能越来越重。目前，多数未到期美国国债的期限都非常短，让情况变得更加棘手，因为这就意味着美国政府要在更短的时间内归还借款。财政部的新数据表明，2013财年美国政府必须偿还的到期债务约为7.5万亿美元（46.09万亿元人民币），这在公众持有的全部可流通美国债券中所占的比例高达65%。客观地看，美国政府的全年收入估计为2.7万亿美元（16.59万亿元人民币），只占须偿还债务的一小部分。这就是说，美国政府需要通过举新债来还旧债。最终，美国政府在这个财年发行了约8.3万亿美元（51.00万亿元人民币）国债。偿还债务后，它将剩余资金用来弥补预算赤字——没错，就算美国政府节衣缩食，预算赤字依然这么高。

    不过，倘若美国未能按时支付债券利息，世界末日就要来了吗？所有人似乎都这么想。但如果我告诉你美国政府曾多次违约呢？到现在美国政府也没有消失，而且还能回首往事。1979年，美国政府也曾处在即将触及债务上限的紧要关头，当时财政部“意外”造成了部分债务的违约。具体情况是，当年4-5月份，财政部没能按期完成三次大规模债券赎回。它把这项“失误”归咎于国会未能投票决定提高债务上限，同时也和技术故障有关。根据上周启用的医保交易网站判断，21世纪的美国政府似乎依然面临着技术问题。

    这次违约事件并没有导致世界末日，但政府也不是完全没有受到任何影响。经济学家特里•齐夫尼和理查德•马库斯对这次事件的分析表明，第一批债券违约后，利率陡然上升了0.6个百分点，而且在随后几个月中一直居高不下。这就是说，和不违约的正常情况相比，美国政府必须付出更多利息。这就是政府关门所产生的恐怖副作用，利率可能需要几周、甚至几个月的时间才能回到正常水平。受此影响，美国纳税人支付了更多的利息。如果国会没有让市场受到不必要的惊吓，情况就不会如此。政府问责办公室（Government Accountability Office）估算，受2011年债务上限论战的直接影响，美国政府当年支付的“额外”利息达13亿美元（79.89亿元人民币）。非营利智囊机构Bipartisan Policy Center提供的数据显示，从债券发行到债券到期，政府将要支付的“额外”利息估计为189亿美元（1161.40亿元人民币）。

    目前，国债利息只占美国联邦政府收入的8%左右。这就是说，如果提前做出规划，同时将债券持有人的偿还优先级排在其他债权人之前，财政部就有可能偿付所有债务，从而避免违约。它同时也意味着，如果需要稍稍违约那么一、两次，美国也许有能力承担远高于目前水平的利息。就1979年的情况来看，美国政府似乎可以略微暂缓债务偿还事宜，从而拿出钱来给老奶奶发放社保，这种做法至少可以保持到债务上限问题得到解决之前。最终，美国政府还是要承担违约带来的额外利息，而且还要为随后发行的所有债券支付一笔数额不定的利息，以覆盖美国国债——这一曾被视为“无风险”证券的新增风险。目前还不清楚，在违约情况下“额外”利息能给投资者带来多少收益。市场也许不会受到什么影响，投资者也可能继续毫不迟疑地购买美国国债。但另一种可能情况是，投资者决定把他们的资金投入“更安全”的证券，从而集体抛弃美国国债。

    That's a big worry because the government has to continuously replace or "roll over" maturing bonds with fresh new ones every month or risk drowning in debt. This is made worse by the fact that the majority of Treasuries outstanding today have very short maturities, meaning that the government must return the money it borrowed sooner rather than later. New figures from the U.S. Treasury show that the government had to replace some $7.5 trillion in debt that matured in fiscal 2013. That was equal to a whopping 65% of all marketable U.S. debt held by the public. To put that number in perspective, the U.S. only brought in an estimated $2.7 trillion in revenue during that whole year, a mere fraction of the debt it had to pay off. This means the government needed to issue new debt to cover the old debt. The government ended up selling some $8.3 trillion in Treasuries during the year. The leftover cash went to fund the budget deficit -- yes, the budget deficit was still that big, even after the "sequester."

    But if the U.S. missed a bond payment would it be the end of the world? Everyone seems to think so. Yet what if I told you that the U.S. once defaulted multiple times on its debt -- and lived to tell about it. In 1979, in the midst of another debt limit showdown, the Treasury ended up "accidentally" defaulting on a portion of its debt. In all, the Treasury missed three major bond redemptions during April and May of that year. The Treasury blamed the "mistake" on the failure of Congress to reach a decision on raising the debt ceiling. It also blamed it on technical glitches, which, judging by the launch of the health exchange websites last week, seems to still be an issue for the government in the 21st century.

    The world didn't end as a result of that default but the government didn't get away scot-free, either. After the first missed payment interest rates jumped by 60 basis points and remained elevated for several months, according to an analysis of the events by economists Terry Zivney and Richard D Marcus. This meant that the government had to pay more interest than it would have normally been the case had it not defaulted. This is the terrible by-product of these government showdowns, it could take weeks or months to bring interest rates back down to earth. As a result, the U.S. taxpayer ends up paying more interest than it would have if Congress hadn't unnecessarily scared the markets. The Government Accountability Office estimates that the government paid $1.3 billion in "extra" interest in 2011 as a direct result of the squabbling over the debt ceiling that year. Over the full maturity of the bonds the government will end up paying an estimated $18.9 billion in "extra" interest, according to the Bipartisan Policy Center.

    Currently, interest payments on the nation's bonds equates to around just 8% of federal revenues. That means if the Treasury plans ahead and was able to prioritize bondholders over all other creditors, it could probably cover all its debt payments and avoid a default. At the same time it also means that the U.S. could afford to pay significantly more in interest if it needed to, say, do a little default or two. Based on what occurred in 1979, it seems possible that the U.S. could put off paying its debt for a bit, allowing the government to pay grandma's social security, at least until the debt situation is worked out. It would eventually have to pay extra interest on the missed bond payments and payout an undetermined amount of interest on all future bonds to account for the increased risk in a security that was once considered "risk-free." It is unclear how much investors could earn in "extra" interest as a result of a default. The markets may shake this all off and investors could go on buying Treasuries without a hitch. But there is a chance that investors might choose to park their cash in "safer" securities and abandon Treasuries all together.