The United States is $20 trillion in debt. That amount of money can never be paid back given current tax revenue and government spending. Whether or not it is even possible to pay it off by cutting spending is debatable. Regardless, no one in power has the political will to cut spending, so it's a non-issue. Therefore, that debt will likely never be paid back at today's dollar values. There are two solutions: 

- Option 1: They can default by choosing not to pay back bond holders. This would be catastrophic and lead to a complete government shut down and deleveraging of all debt. Interest rates would likely spike as the risk lending to the USA would be to high in light of a destroyed credit rating.

- Option 2: They can inflate the debt away and continue to devalue the dollar through artificially low interest rates and QE. The money supply will increase, the buying power of dollars will decline, and $20 trillion can be paid back relatively easily, although the USA's creditors will be pissed because in terms of the buying power of their bond values, they will essentially be worthless.

Option 2 is the current path the Fed is going down and why I do not expect them to voluntarily raise interest rates (the default path). Inflating the debt away is the most politically expedient because those in power do not need to take responsibility, but instead can blame someone or something else. 

Do you see a third option?