The fact that a problem has national security implications doesn't mean the military is the best equipped to deal with it. The military's designed to deal with a specific type of national security problem: other militaries. But if, for example, we find out that So-and-So has likely been providing financial support to terrorists, we don't send the Army in after him, even though it's clearly a national security matter. I think it's the same along the border. If there's no army to fight, civilian law enforcement is capable of handling the job.
I understand...it's just this whole ILLEGAL INVASION of our country gets my blood boiling.