Final answer:
Theodore Roosevelt was appointed as Vice President to William McKinley between 1901 to 1903 but became the President in 1901 after McKinley's assassination, marking a new era of progressive politics.
Step-by-step explanation:
Between 1901 to 1903, Theodore Roosevelt was appointed as the Vice President to President William McKinley.
After McKinley's assassination in 1901, Roosevelt became the youngest president in the nation's history.
His unexpected rise to the presidency marked the beginning of a new era of progressive national politics and profoundly transformed the role of the presidency for the twentieth century.
Roosevelt continued to make his mark on history by taking on big business and protecting federal lands, setting a precedent for his successors.