Why does Obama continue to blame Bush? Because (fill in the blank)

Ratios of deficit to GDP for the past five presidents:

Ronald Reagan
1981-88 4.2 %
1982-89 4.2
Average 4.2

George H. W. Bush
1989-92 4.0
1990-93 4.3
Average 4.2

Bill Clinton
1993-2000 0.8
1994-2001 0.1
Average 0.5

George W. Bush 

2001-08 2.0
2002-09 3.4
Average 2.7

Barack Obama
2009-12* 9.1
2010-12 8.7
Average 8.9
*fiscal 2012 ends Sept. 30, 2012, so this figure is estimated

Forbes