Gail Heriot on Instapundit:
AND TYLER TOO: President William Henry Harrison died on this day in 1841, only 31 days into his term. He was the first President to die in office. Here’s the Constitutional quirk: In those days, the Constitution simply said that in case of the President’s death “the Powers and Duties of the said office” “shall devolve upon the Vice President.” It didn’t say that the Vice President BECOMES the President. Tyler, however, took the position that he WAS then the President, and got royally (or at least presidentially) pissed off when some people disagreed. It wasn’t until the 25th Amendment, ratified in 1967, that it was made clear that the Vice President actually becomes the President upon the death, resignation or removal of the President.