This close to a presidential election, an event that only happens every four years, one can hope to be excused for obsessing over the "inside baseball" details of politics. I just read a column by Steven Hayward at Power Line which gets relatively deep into the intricacies of presidential succession.
There is a law - the Presidential Succession Act of 1947 - under which the Speaker of the House would become acting president in the event that the results of the election were still under contention and the terms of Trump and Pence had ended. There is also wording in the Constitution to the effect that no member of the Congress can serve in any executive branch position, which includes the presidency.
Constitutional scholars have argued that, as the Speaker is a member of Congress, the aforementioned succession act is unconstitutional. It has never been challenged in court as an occasion for its use has not arisen and therefore no one has had standing to challenge it.
Early in 2021 an occasion for its use could arise, and if it is then found unconstitutional, we could see a President Pompeo as the Secretary of State is the first among equals in the cabinet. Cabinet jobs, it is alleged, do not automatically end when the President's term ends.
Imagine the turmoil if a "president" Pelosi appointed acting cabinet members and the sitting cabinet refused to step down, alleging that her accession was unconstitutional. You think SCOTUS has made important decisions in the past? Imagine living through this scenario.
Stay tuned. We live in very interesting times.