While attending the Pan-American Exposition in Buffalo, New York, President William McKinley was assassinated by Leon Czolgosz on September 6, 1901. Although doctors were able to remove the bullet, but his health declined soon thereafter because the medical practice at the time was not familiar with the concept of introducing intravenous fluids, as used in modern medicine. The assassination would bring Theodore Roosevelt into the Presidency, and would mark a major political shift in the White House.