There was a decent episode of West Wing about the 25th. Martin Sheen’s daughter was kidnapped by terrorists and his CoS told him that fact made it impossible to serve as POTUS . He sent the unable to serve message and as there was no VP, the Speaker, a Republican played by John Goodman, became acting POTUS.
I wouldn’t know...I don’t watch network TV...nor live in a fantasy world. What if Martin Sheen didn’t like his daughter?