Whenever
(1) the United States, or any of the Territories, Commonwealths, or possessions, is invaded or is in danger of invasion by a foreign nation;
(2) there is a rebellion or danger of a rebellion against the authority of the Government of the United States; or
(3) the President is unable with the regular forces to execute the laws of the United States;
the President may call into Federal service members and units of the National Guard of any State in such numbers as he considers necessary to repel the invasion, suppress the rebellion, or execute those laws. Orders for these purposes shall be issued through the governors of the States or, in the case of the District of Columbia, through the commanding general of the National Guard of the District of Columbia.
We've been using the Coast Guard for 25 years to keep freedom loving Cubans from coming into Florida.
I have already done two 15 month mobilizations (and I got $1000 a month bonus pay for volunteering to go over 24 months and that bonus is only available overseas), so I can't go again unless I volunteer (not going to happen-already spent too much time away from my wife).