Hmm, that wasn’t numberonepal’s scenario I was referring to, but your comment is interesting and appropriate to the discussion. Maybe you should re-post it now.
An executive order from the Kennedy Administration, kept updated by subsequent administrations, covers a surgical nuclear decapitation strike on DC. The military would work with the states to reconstitute the federal government via special elections (House), gubernatorial appointments (Senate) and convening the Electoral College from the previous presidential election (President and Vice President). Please note that if states withdraw their Electors from that previous presidential election, it comes into play here.
An executive order from the Johnson Administration, kept updated by subsequent administrations, covers a military takeover in the event of massive civil disturbance, i.e., race war. It covers rescheduling elections of all kinds until order can be restored and the Constitution reinstated. This EO was almost invoked in 1992 during the Rodney King insurrections. Please note that this EO provides for the use of internment camps, which today are run by FEMA.