Wasn't this why the National Guard was created?

To avoid conflict with the Posse Comitatus Act?:

The U.S. military expects to have 20,000 uniformed troops inside the United States by 2011 trained to help state and local officials respond to a nuclear terrorist attack or other domestic catastrophe, according to Pentagon officials.

The long-planned shift in the Defense Department's role in homeland security was recently backed with funding and troop commitments after years of prodding by Congress and outside experts, defense analysts said.

There are critics of the change, in the military and among civil liberties groups and libertarians who express concern that the new homeland emphasis threatens to strain the military and possibly undermine the Posse Comitatus Act, a 130-year-old federal law restricting the military's role in domestic law enforcement.

But the Bush administration and some in Congress have pushed for a heightened homeland military role since the middle of this decade, saying the greatest domestic threat is terrorists exploiting the proliferation of weapons of mass destruction.

[snip]

Domestic emergency deployment may be "just the first example of a series of expansions in presidential and military authority," or even an increase in domestic surveillance, said Anna Christensen of the ACLU's National Security Project. And Cato Vice President Gene Healy warned of "a creeping militarization" of homeland security.

"There's a notion that whenever there's an important problem, that the thing to do is to call in the boys in green," Healy said, "and that's at odds with our long-standing tradition of being wary of the use of standing armies to keep the peace."

The National Guard:

Established under Title 10 and Title 32 of the U.S. Code, state National Guard serves as part of the first-line defense for the United States.[3] The state National Guard is divided up into units stationed in each of the 50 states and U.S. territories and operates under their respective state governor or territorial government [4]. The National Guard may be called up for active duty by the state governors or territorial commanding generals to help respond to domestic emergencies and disasters, such as those caused by hurricanes, floods, and earthquakes.[4]

With the consent of state governors, members or units of state National Guard may be appointed to be federally recognized armed force members in active or inactive service [5][6][7]. If so recognized, they become part of the National Guard of the United States [1]. The National Guard of the United States units or members may be called up for federal active duty in times of Congressionally sanctioned war or national emergency [4]. State National Guard may also be called up for federal service, with the consent of state governors, to repel invasion, suppress rebellion, or execute federal laws if the United States or any its states or territories are invaded or is in danger of invasion by a foreign nation, or if there is a rebellion or danger of a rebellion against the authority of the federal government, or if the President is unable with the regular armed forces to execute the laws of the United States [8]. Because both state National Guard and the National Guard of the United States relatively go hand-in-hand, they are both usually referred to as just National Guard.

Maybe I've answered my own question: (my bold)

The Posse Comitatus Act and the Insurrection Act substantially limit the powers of the federal government to use the military for law enforcement.

The Posse Comitatus Act is a United States federal law (18 U.S.C. § 1385) passed on June 16, 1878 after the end of Reconstruction. The Act prohibits most members of the federal uniformed services (the Army, Air Force, and State National Guard forces when such are called into federal service) from exercising nominally state law enforcement, police, or peace officer powers that maintain "law and order" on non-federal property (states and their counties and municipal divisions) in the former Confederate states.

The statute generally prohibits federal military personnel and units of the National Guard under federal authority from acting in a law enforcement capacity within the United States, except where expressly authorized by the Constitution or Congress. The Coast Guard is exempt from the Act.

Any militarization of our country is a dangerous thing and needs to be controlled carefully.