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, most notably refusing to reappoint Louis F. Payn as state Insurance Superintendent because he was widely seen as a corrupt associate of Platt. 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 Matthew Quay proposed to get Roosevelt out of Platt's way in New York by nominating him for vice president. Party boss Mark Hanna was horrified by the proposition, stating "Why, everybody's gone crazy! What is the matter with all of you? Here's this convention going headlong for Roosevelt for Vice President. Don't any of you realize that there's only one life between that madman and the Presidency? Platt and Quay are no better than idiots! What harm can he do as Governor of New York compared to the damage he will do as President if McKinley should die?" But since Hanna was unable to convince President McKinley to refuse Roosevelt as his Vice President, his efforts were in vain. Roosevelt was chosen by acclamation, and played a major part in McKinley's re-election, and became president in September 1901 after McKinley was assassinated in office.