Republican progressives reconvened in Chicago's Orchestra Hall and endorsed the formation of a national Progressive Party. When formally launched that summer, the new party chose Roosevelt as its presidential nominee. Questioned by reporters, Roosevelt said he felt as strong as a "bull moose." From that time forward, the Progressives became known as the Bull Moose Party and promised to increase federal regulation and protect the welfare of ordinary Americans.
You can read the full story of what happened on that day in Today in History, the Library's Web site that offers fascinating details about what happened in the past for every day of the year.