Specifically Article 2 section 2 states
"The President shall be Commander in Chief of the Army and Navy of the United States, and of the Militia of the several States, "
The extremists militia. Are a clear and present danger to the safety of the U.S. And are actively/passively engaged in domestic terrorism. Being referred to as vanila isis and other names.
As we saw when one was killed and several were arrested. Many ran scared from the federal reserve. In some cases leaving their guns. When they realize being in a militia means they are subordinate to the President. The ones killed overseas by their fellow terrorists will not be a threat. And the ones left here may just find being a homegrown terrorist is just not for them.