Steven Kosiak at the Center for Strategic and Budgetary Assessments (CSBA) has released a solid analysis today that tries to measure total federal funding for defense, homeland security, and national security since 9/11. The full analysis can be downloaded at this link.
Kosiak finds a total net increase of $754 billion in federal spending since 9/11 above expected baseline pre-9/11 spending, adjusted for the rate of inflation. Of that total, he estimates that approximately one-third has gone for the war in Iraq, and one-third for national security spending that has little or nothing to do with the war on terror.
The remaining third, for activities directly related to 9/11, includes spending for the war in Afghanistan, recovery from the attacks, and homeland security.
Kosiak calculates the total net and cumulative homeland security spending attributable to 9/11 to be equal to $146 billion, of which $34 billion went to the DOD for homeland defense activities, and the remaining $112 billion for civilian homeland security activities.
This $112 billion represents approx. a doubling of homeland security spending above the pre-9/11 baseline, when adjusted for inflation.
This is solid analysis and is worth a read.