????這可是個大問題，原因是政府每個月都必須用新債券來代替到期債券，或者說實現“轉滾”，否則政府的債務負擔就可能越來越重。目前，多數未到期美國國債的期限都非常短，讓情況變得更加棘手，因為這就意味著美國政府要在更短的時間內歸還借款。財政部的新數據表明，2013財年美國政府必須償還的到期債務約為7.5萬億美元（46.09萬億元人民幣），這在公眾持有的全部可流通美國債券中所占的比例高達65%?？陀^地看，美國政府的全年收入估計為2.7萬億美元（16.59萬億元人民幣），只占須償還債務的一小部分。這就是說，美國政府需要通過舉新債來還舊債。最終，美國政府在這個財年發行了約8.3萬億美元（51.00萬億元人民幣）國債。償還債務后，它將剩余資金用來彌補預算赤字——沒錯，就算美國政府節衣縮食，預算赤字依然這么高。

????不過，倘若美國未能按時支付債券利息，世界末日就要來了嗎？所有人似乎都這么想。但如果我告訴你美國政府曾多次違約呢？到現在美國政府也沒有消失，而且還能回首往事。1979年，美國政府也曾處在即將觸及債務上限的緊要關頭，當時財政部“意外”造成了部分債務的違約。具體情況是，當年4-5月份，財政部沒能按期完成三次大規模債券贖回。它把這項“失誤”歸咎于國會未能投票決定提高債務上限，同時也和技術故障有關。根據上周啟用的醫保交易網站判斷，21世紀的美國政府似乎依然面臨著技術問題。

????這次違約事件并沒有導致世界末日，但政府也不是完全沒有受到任何影響。經濟學家特里?齊夫尼和理查德?馬庫斯對這次事件的分析表明，第一批債券違約后，利率陡然上升了0.6個百分點，而且在隨后幾個月中一直居高不下。這就是說，和不違約的正常情況相比，美國政府必須付出更多利息。這就是政府關門所產生的恐怖副作用，利率可能需要幾周、甚至幾個月的時間才能回到正常水平。受此影響，美國納稅人支付了更多的利息。如果國會沒有讓市場受到不必要的驚嚇，情況就不會如此。政府問責辦公室（Government Accountability Office）估算，受2011年債務上限論戰的直接影響，美國政府當年支付的“額外”利息達13億美元（79.89億元人民幣）。非營利智囊機構Bipartisan Policy Center提供的數據顯示，從債券發行到債券到期，政府將要支付的“額外”利息估計為189億美元（1161.40億元人民幣）。

????目前，國債利息只占美國聯邦政府收入的8%左右。這就是說，如果提前做出規劃，同時將債券持有人的償還優先級排在其他債權人之前，財政部就有可能償付所有債務，從而避免違約。它同時也意味著，如果需要稍稍違約那么一、兩次，美國也許有能力承擔遠高于目前水平的利息。就1979年的情況來看，美國政府似乎可以略微暫緩債務償還事宜，從而拿出錢來給老奶奶發放社保，這種做法至少可以保持到債務上限問題得到解決之前。最終，美國政府還是要承擔違約帶來的額外利息，而且還要為隨后發行的所有債券支付一筆數額不定的利息，以覆蓋美國國債——這一曾被視為“無風險”證券的新增風險。目前還不清楚，在違約情況下“額外”利息能給投資者帶來多少收益。市場也許不會受到什么影響，投資者也可能繼續毫不遲疑地購買美國國債。但另一種可能情況是，投資者決定把他們的資金投入“更安全”的證券，從而集體拋棄美國國債。

????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.