Posse Comitatus wasn't in effect during Katrina, fat head.
Don't feel too bad though, Stench didn't know either.
The Posse Comitatus Act is a United States federal law (18 U.S.C. § 1385, original at 20 Stat. 152) signed on June 18, 1878 by President Rutherford B. Hayes. The purpose of the act – in concert with the Insurrection Act of 1807 – is to limit the powers of the federal government in using its military personnel to act as domestic law enforcement personnel. The PCA does not completely prohibit, nor prevent the use of the military from performing law enforcement. The President does have two direct constitutional exceptions to the PCA, identified in Title 32, Section 215.4 of the Code of Federal Regulations: emergency authority and protection of Federal property and functions.
Indirect involvement of the military in law enforcement activities is permitted as long as the military has “not subjected civilians to the exercise of military power that is regulatory, proscriptive, or compulsory in nature.”
This allows the military to provide equipment, transportation, training, supplies, and services to law enforcement officials as long as it does “not directly and actively participate in law enforcement tasks.”
Congress also enacted specific exceptions to the PCA allowing the military to provide disaster relief and protection of public health and safety under the Robert T. Stafford Disaster Relief Act enacted in Title 42 U.S.C. Section 5170b.
The Stafford Act (signed in 1988) gives the President broad discretion to find that a major disaster exists, requiring emergency response after a declaration request from the Governor of the affected state.
Once the President has declared an emergency or major disaster and invoked the Stafford Act, the Governor of the affected state can request use of the resources of the DoD for emergency work that is essential for the preservation of life and property.
The DoD can provide military support to include clearance and removal of debris and wreckage, and temporary restoration of essential public facilities and services for up to 10 days under the Stafford Act.