There are multiple answers to your question.
President Trump federalized a million national guard troops.
The military can be brought in to work with government agencies in times of great peril to our nation.
When Continuity of Government is in place, there are a lot of things happening that you don’t see.
The purpose of the Constitution is the continuity of liberty, not Continuity of Government. I don't give a hang about the excuse, it's power so easily abused that it will easily be used against the people on behalf of the fascist Deep State.