Mostly Bush's Debt

Furthermore, Obama's share of the debt wouldn't exist if Bush hadn't ruined the economy.

in reference to:

"All told, Obama-era choices account for about $1.7 trillion in new debt, according to a separate Washington Post analysis of CBO data over the past decade. Bush-era policies, meanwhile, account for more than $7 trillion and are a major contributor to the trillion-dollar annual budget deficits that are dominating the political debate."
- Running in the red: How the U.S., on the road to surplus, detoured to massive debt - The Washington Post (view on Google Sidewiki)