The amount of debt the US is allowed to have is set by Congress (American Parliament) and so has to be decided by both the Republicans (Conservatives) and Democrats (Labour).

In 2011 the US was coming up to its debt ceiling (the maximum amount of money the government is allowed to borrow), if Congress weren’t to agree for the ceiling to be raised then the US may have to default on its obligations (interest payments to debtors as well as payments to civil servants and social services etc).
We can see from the graph (source BBC News) to the left that in recent times all Presidents have increased the debt ceiling and borrowed money from international markets (particularly Chinese markets). [...]