Theodore Roosevelt is widely regarded as the first modern President of the United States. The stature and influence that the office has today began to develop with TR. Throughout the second half of the 1800s, Congress had been the most powerful branch of government. And although the presidency began to amass more power during the 1880s, Roosevelt completed the transition to a strong, effective executive. He made the President, rather than the political parties or Congress, the center of American politics.

Roosevelt did this through the force of his personality and through aggressive executive action. He thought that the President had the right to use any and all powers unless they were specifically denied to him. He believed that as President, he had a unique relationship with and responsibility to the people, and therefore wanted to challenge prevailing notions of limited government and individualism; government, he maintained, should serve as an agent of reform for the people.

His presidency endowed the progressive movement with credibility, lending the prestige of the White House to welfare legislation, government regulation, and the conservation movement. The desire to make society more fair and equitable, with economic possibilities for all Americans, lay behind much of Roosevelt's program. The President also changed the government's relationship to big business. Prior to his presidency, the government had generally given the titans of industry carte blanche to accomplish their goals. Roosevelt believed that the government had the right and the responsibility to regulate big business so that its actions did not negatively affect the general public. However, he never fundamentally challenged the status of big business, believing that its existence marked a naturally occurring phase of the country's economic evolution.

Roosevelt also revolutionized foreign affairs, believing that the United States had a global responsibility and that a strong foreign policy served the country's national interest. He became involved in Latin America with little hesitation: he oversaw the Panama Canal negotiations to advocate for U.S. interests and intervened in Venezuela and Santo Domingo to preserve stability in the region. He also worked with Congress to strengthen the U.S. Navy, which he believed would deter potential enemies from targeting the country, and he applied his energies to negotiating peace agreements, working to balance power throughout the world.

Even after he left office, Roosevelt continued to work for his ideals. The Progressive Party's New Nationalism in 1912 launched a drive for protective federal regulation that looked forward to the progressive movements of the 1930s and the 1960s. Indeed, Roosevelt's progressive platform encompassed nearly every progressive ideal later enshrined in the New Deal of Franklin D. Roosevelt, the Fair Deal of Harry S. Truman, the New Frontier of John F. Kennedy, and the Great Society of Lyndon B. Johnson.

In terms of presidential style, Roosevelt introduced "charisma" into the political equation. He had a strong rapport with the public and he understood how to use the media to shape public opinion. He was the first President whose election was based more on the individual than the political party. When people voted Republican in 1904, they were generally casting their vote for Roosevelt the man instead of for him as the standard-bearer of the Republican Party. The most popular President up to his time, Roosevelt used his enthusiasm to win votes, to shape issues, and to mold opinions. In the process, he changed the executive office forever.