According to the US Constitution this is the Presidential Order of Succession.
VP, Speaker of the House, President pro Tempore of the Senate, SOS, etc.
Let’s say JB is arrested tomorrow. How would the SOH not be installed on Jan 20? If NP’s arrested too does Grassley become POTUS?
Does Martial Law suspend the USC? Does FEMA control suspend the USC?
Let’s talk about the scenarios.
Twentieth Amendment Section 3 - The VP elect is sworn in if the President elect dies (VPe assumes duties) or “fails to qualify” (VPe acts as President until one qualifies). But I don’t think we’ll need to worry too much about Biden, Harris, Pelosi, or Grassley being sworn in.