The Constitution has pretty clear guidance on what to do if a president becomes incapacitated or dies while in office, as laid out in the 25th Amendment.
It’s unclear what effect the diagnosis will have on the election, said Cornell Clayton, the director of the Thomas S. Foley Institute for Public Policy and Public Service at Washington State University. A total of eight U.S. presidents have died in office, four of natural causes and four by the hand of an assassin. None of them became ill or were killed so close to an election day.
There’s a clear line of succession laid out in federal law if a president becomes incapacitated before an election, Clayton said.
“I don’t think there’s any problem about who’s going to be in charge,” Clayton said. “We know that; there’s a process for that.”