Half of that was for their vacations.
Check it out:

The debt of the U.S. government has increased $6.666 trillion since President Barack Obama took office on Jan. 20, 2009, according to the latest numbers released by the Treasury Department.

When President Obama was first inaugurated on Jan. 20, 2009, the debt of the U.S. government was $10,626,877,048,913.08, according to the Treasury Department’s Bureau of the Public Debt. As of Jan. 31, 2014, the latest day reported, the debt was $17,293,019,654,983.61—an increase of $6,666,142,606,070.53 since Obama’s first inauguration.