World's fairs have witnessed marvelous debuts – and melancholy demises. At the 1901 Pan American Exposition, President William McKinley (shown above) was shaking hands with attendees when anarchist Leon Czolgosz shot him twice. Had doctors taken him to the new X-ray machine displayed at the expo to assess the damage, McKinley might have lived. But after the physicians moved him to a makeshift room on the fairgrounds, they worried moving him again would hasten his death. Thus, McKinley died at the fair, and Vice President Theodore Roosevelt ascended the nation's highest office.