https://www.nysun.com/editorials/president-pelosi/91232/
President Trump’s warning to a conservative gathering that before this election is resolved the person who could next emerge as President is Nancy Pelosi, well, it’s a startling point. It’s not entirely idle, though. The Constitution, and legislation it grants the Congress the power to pass, both envision a situation where the Speaker could automatically become president at 12:01 p.m. o’clock on January 20.
Neither Mr. Trump, as we understand him, nor we are saying such an event is likely. Just possible. Were it to come to pass, though, it would be completely — to the degree that there is such a constitutional concept — kosher. That’s because of the 20th Amendment. It says that the “terms of the President and Vice President shall end at noon on the 20th day of January,” no ifs, ands, or buts.
It also says that the terms of the Senators and Congressmen end at noon on January 3. That means the 116th Congress ends and the 117th begins 17 days before Mr. Trump’s term is up. That gives the Representatives House time to choose its Speaker. It’s likely — not certain, we suppose — to be Mrs. Pelosi, making her next in line for the presidency after Vice President Pence.
The 20th Amendment also particularizes what happens if certain complications arise. If either the President or President-elect shall have died, say, the Vice President elect “shall become President.” Then it says what happens “if a President shall not have been chosen before the time fixed for the beginning of his term, or if the President elect shall have failed to qualify.”