US Code
CHAPTER 1211— NATIONAL GUARD MEMBERS IN FEDERAL SERVICE
§ 12406. National Guard in Federal service: call

(1) the United States, or any of the 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;

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