We all know the Presidential line of succession from our elementary school civics class: If the President dies or is incapacitated, the Vice President takes over; if the VP is then incapacitated, the Speaker of the House takes over, then the President pro tempore of the Senate, then the Secretary of State, then other Cabinet officers. Simple, right? Well, not so fast.
The 25th Amendment to the U.S. Constitution specifies the exact process for declaring a President (or acting President) incapacitated: The President can inform the President pro tem of the Senate and the Speaker of the House, in writing, that he is incapacitated, at which point succession is activated. Or, the VP and a majority of the Cabinet can provide that written declaration.
Of course, this Story is in the context of President Trump's positive COVID test. So suppose Trump becomes incapacitated (but remains alive), e.g. unconscious on a ventilator. If he doesn't provide a written declaration of incapacity to Congressional leaders, VP Pence and a majority of the Cabinet can do so. No problem.
But what happens if Pence then falls ill? He hasn't exactly been a model citizen of social distancing and demanding mask wearing. If he becomes incapacitated, but is unwilling to provide written declaration of his incapacity before he becomes physically unable to do so, the 25th Amendment can't apply: There's no way to carry out the process it specifies, since there’s no Vice President to provide the declaration along with a Cabinet majority.
So the situation is then governed by Article II, Section 1 of the Constitution:
In Case of the Removal of the President from Office, or of his Death, Resignation, or Inability to discharge the Powers and Duties of the said Office, the Same shall devolve on the Vice President, and the Congress may by Law provide for the Case of Removal, Death, Resignation or Inability, both of the President and Vice President, declaring what Officer shall then act as President, and such Officer shall act accordingly, until the Disability be removed, or a President shall be elected.
But who determines "inability"? The 25th Amendment was supposed to clarify that, but it doesn't seem to cover this situation. Can Nancy Pelosi just declare that Pence is unable to discharge his duties, and become acting President? Would she need to sue for that declaration in Federal court? Would the case need to start with the District Court and wind its way through the appeals process, or could it go directly to the Supreme Court? (And let’s remember that SCOTUS could wind up in a 4–4 tie.) How would the case be resolved—could a judge just demand a Zoom session with Pence to see for themselves? And what if Trump administration officials don't cooperate with the process, and continue to claim that Pence is well enough to serve, even if that's not true?