[236] After the assassination, the present United States Secret Service came into existence when the Congress deemed it necessary that presidential protection be part of its duties.[237]
A controversial aspect of McKinley's presidency is territorial expansion and the question of imperialism; with the exception of the Philippines, granted independence in 1946, the United States retains the territories taken under McKinley.[238] The territorial expansion of 1898 is often seen by historians as the beginning of American empire.[239] Morgan sees that historical discussion as a subset of the debate over the rise of America as a world power; he expects the debate over McKinley's actions to continue indefinitely without resolution, and notes that however one judges McKinley's actions in American expansion, one of his motivations was to change the lives of Filipinos and Cubans for the better.[240]
Morgan alludes to the rise of interest in McKinley as part of the debate over the more assertive American foreign policy of recent decades:

McKinley was a major actor in some of the most important events in American history. His decisions shaped future policies and public attitudes. He usually rises in the estimation of scholars who study his life in detail. 