The US debt was 10 trillion when Obama took office. And now it's 16 trillion. But Obama's got another 4 years left. In other words he'll easily be able to add AT LEAST another 4 trillion without breaking a sweat. That's just how good he is.
Long story short, the debt will have more than doubled under him. Historic president indeed. :D
DISCLAIMER: No Obama did not personally spend that 6 and a half trillion.