The 926 delegates to the Republican convention , which met in Philadelphia on June 19 – 21 , re-nominated William McKinley by acclamation . Thomas C. Platt , the " boss " of the New York State Republican Party , did not like Theodore Roosevelt , New York 's popular governor , even though he was a fellow Republican . Roosevelt 's efforts to reform New York politics – including Republican politics – led Platt and other state Republican leaders to pressure President McKinley to accept Roosevelt as his new vice - presidential candidate , thus filling the spot left open when Vice President Garret Hobart died in 1899 . By electing Roosevelt vice president , Platt would remove Roosevelt from New York state politics . Although Roosevelt was reluctant to accept the nomination for vice president , which he regarded as a relatively trivial and powerless office , his great popularity among most Republican delegates led McKinley to pick him as his new running mate . Quite unexpectedly , Roosevelt would be elevated to the presidency in September 1901 , when McKinley was assassinated in Buffalo , New York
Republican convention
1900 Republican National Convention
1900 United States presidential election