Trump has blustered his way through the age issue so far, but he has never given an honest accounting of his physical state. American politics is littered with examples of death intruding abruptly on our political leadership, changing the course of history in the process. One person who must understand it is Biden, whose long life has been convulsed over and over by searing tragedy. If anyone in American politics knows that death keeps its own calendar, it is him. If leaving office means accepting the inevitability of death, then you can start to see the appeal of running again.