Platt reluctantly supported Theodore Roosevelt 's candidacy for Governor of New York in 1898 , in the immediate aftermath of Roosevelt 's fame leading the Rough-Riders in the Spanish – American War earlier that year . Once elected , Governor Roosevelt was independently minded , and crusaded against machines and corruption . In response , Platt sought a way to " shelve " Roosevelt so that a more compliant Governor could be installed in his place . President William McKinley 's original vice president had died in office , leaving a place on the ticket to fill before the 1900 election . At the 1900 Republican National Convention , Platt and President McKinley 's political ally Mark Hanna proposed to get Roosevelt out of Platt 's way in New York by nominating him for vice president . Roosevelt was chosen by acclamation , played a major part in McKinley winning re-election , and became president in September 1901 after McKinley was assassinated in office
1900 Republican National Convention
1900 Republican National Convention
Thomas C. Platt