How have American presidents used their position to increase the power of the office?
The power of the president, and the executive branch in general, has increased significantly over the history of the United States. A number of presidents have taken actions that greatly expanded the powers of their office. This has happened in several ways.
Andrew Jackson was the first president to make extensive use of his powers. Although he did not add anything to them that was not already spelled out in article II of the US Constitution, he made it a regular habit to employ his veto power. In fact, he issued far more vetoes than any previous president. Where President Jackson really expanded the power of the president was by establishing a cult of personality. He used his charisma to gain a large following among the masses which helped propel him politically and strengthen the party system in the country.
Few presidents expanded the power of their office more than Abraham Lincoln. The Civil War created a situation in which Lincoln felt it necessary that the president be able to act quickly and unilaterally. Without first securing agreements from Congress, Lincoln expanded the size of the military and ordered it into action by blockading Southern ports. He even suspended the writ of habeas corpus, which allowed him to have dissidents arrested and jailed. Many of the expansions of power that Lincoln put in place were retracted after the Civil War, but it set a precedent in which the president could take swift action in times of crisis.
Theodore Roosevelt expanded the power of the president in its role in international relations. On multiple occasions, he brokered peace agreements with feuding foreign powers. He also used the role of chief executive to meddle more directly in foreign affairs, such as ordering the navy to prevent Colombia from stopping the Panamanian independence movement.
As a part of his New Deal programs, President Franklin Roosevelt increased the power of the president to make widespread economic decisions. The role of various federal bureaus were expanded which allowed the president to enforce economic regulatory measures like never before.
In more recent years, President George W. Bush increased the president's power over implementing new laws with his use of signing statements. Signing statements had been around for a long time. They were usually issued by a president when he signed a bill as a way to congratulate the legislative effort. President Bush changed their use by using them to challenge certain parts of the bill, effectively saying that the executive branch would not enforce particular parts of the law.
There are other ways in which presidents have strengthened their powers over the years. The important thing to remember is that once a new power is achieved, it becomes usually precedent for future presidents.