When exactly does the vice president become president when the chief executive dies?

When John F. Kennedy was assassinated in November 1963, Lyndon Johnson thought he wasn’t president until he took the oath of office. He believed the United States did not have a chief executive for more than an hour after Kennedy’s death. (Doctors pronounced JFK dead at 1 pm CST. Johnson took the oath at 2:38.)

But according to the Constitution — at least, the accepted reading of it at the time — Johnson became president the moment JFK died. By the time Johnson was sworn in, he had been president for 98 minutes. Some of Johnson’s advisors told him that, but he wasn’t sure. He rushed to take the oath so there would be no questions.

And the only reason LBJ was the chief executive in power and in name was because of the stubbornness of another president 122 years before.

This leads us to the sticky presidential succession issue that went unresolved for a long time.

When President William Henry Harrison died in 1841, Vice President John Tyler insisted he had assumed the powers, the duties, and the title. But some Senators considered him only a placeholder. They referred to him as “acting president,” and said he was still vice president in name.

The wording of the Constitution was so vague on this point that neither side could prove their case. But Tyler’s stubborn view eventually became the unofficial precedent. He was so insistent that he returned unopened any correspondence addressed to him as vice president.

The Constitution didn’t settle the issue until the 25th amendment in 1967.