The U.S. debt is usually analyzed in terms of gross domestic product vs. amount owed (debt), a percentage in other words. At the beginning of Clinton's presidency the percentage of debt to GDP was 49.5%, and at the end of his presidency it was 34.5%. By the time his presidency ended in 2001 taxes were increased three times. Subsequent to this there were several events that caused the huge debt we see today. The Bush tax cuts account for a huge percentage of the increase, and there were huge increases in presidential discretionary spending that Bush and Obama made use of. The economy has been in a slump for about seven years, so revenue was negatively impacted while expenditures increased (unemployment and other social safety nets). The wars in Afghanistan and Iraq were tremendously expensive. The amount of the interest has gone up because the amount owed is so much more now than in the past. This is why the debt is so high, and this is why many people fear that the interest on the debt will become too much for us to manage, even if we go crazy with taxes and cut out spending with a chainsaw.
The REAL reason we are in the deep stuff is not so much China (they just make everything worse) - it is the fat cats on Wall Street. They invented an insane time-bomb called sub-prime mortgages and everyone went mad trading in bits of paper that were WORTHLESS!!!! When the bubble burst, a couple of Trillion dollars had evaporated. One Broker was ritually sacrificed, while all the others went scot free. Ordinary folk have carried the financial losses, but the fat cats never do. This debacle also hit every other country on the planet, whose economies were being supported on mountains of debt - America sneezes and the rest of the world gets a cold. It has been so forever and will be that way for the next hundred years.
The big government debt has been caused by the accumulation of Federal budget deficits over a very long time. Such has been the case because of the numerous poor economic policies, which have failed to yield any tangible results.