Kammala wannan jumla: Roosevelt ya yi aiki a matsayin mataimakin sakatare na rundunar sojan ruwa da gwamnan New York kafin ya lashe zaben a matsayin William McKinley a matsayin mataimakin shugaban kasa a zaben shugaban kasa na 1900. Roosevelt ya zama shugaban kasa bayan
kisan gillar McKinley da ɗan adawa Leon Czolgosz a Buffalo, New York; Czolgosz ya harbe McKinley a ranar 6 ga Satumba, 1901, kuma McKinley ya mutu a ranar 14 ga Satumba. An rantsar da Roosevelt a ranar mutuwar McKinley a gidan Ansley Wilcox a Buffalo. John R. Hazel, Alkalin Gundumar Amurka na Yammacin Gundumar New York, ya ba da rantsuwar ofishin. Kasancewa 'yan makonni kaɗan daga ranar haihuwarsa ta 43, Roosevelt ya zama shugaban ƙasa mafi ƙanƙanta a tarihin Amurka, bambancin da ya ci gaba da riƙewa.