Presidency of Thomas Jefferson

Thomas Jefferson's tenure as the third president of the United States began on March 4, 1801, and ended on March 4, 1809. Jefferson assumed the office after defeating incumbent president John Adams in the 1800 presidential election. The election was a political realignment in which the Democratic-Republican Party swept the Federalist Party out of power, ushering in a generation of Jeffersonian dominance in American politics. After serving two terms, Jefferson was succeeded by Secretary of State James Madison, also of the Democratic-Republican Party.

Jefferson took office determined to roll back the Federalist program of the 1790s. His administration reduced taxes, government spending, and the national debt, as well as repealed the . He also signed the Military Peace Establishment Act, and adopted an assimilation policy toward Native Americans known as his "civilization program." In 1804, Jefferson appointed William Johnson to the Supreme Court—the first Jeffersonian Republican to serve on the court. In foreign affairs, the major developments were the acquisition of the gigantic Louisiana Purchase from France in 1803, an embargo against trade with both Great Britain and France, and worsening relations with Britain as the United States tried to remain neutral in the midst of the Napoleonic Wars that engulfed Europe. He established a national military academy, used the U.S. Navy to protect merchant ships from Barbary pirates in North Africa, known as the Barbary Wars, and developed a plan to protect U.S. ports from foreign invasion by the use of small gunboats (a plan that proved useless when war came in 1812). He also authorized the to explore the Louisiana Territory and the Pacific Northwest.

During his second term, Jefferson's attention was focused on the trial of then former Vice President Aaron Burr for treason, which resulted in an acquittal, and on the issue of slavery, specifically the importation of slaves from abroad. In 1806, he denounced the international slave trade as a "violation of human rights" and called upon Congress to criminalize it. Congress responded by approving the Act Prohibiting Importation of Slaves the following year. Jefferson appointed Henry Brockholst Livingston and Thomas Todd to the Supreme Court in 1806 and 1807, respectively. The final years of Jefferson's second term were dominated by rising tensions between the United States and Britain, as the Royal Navy began impressing sailors from American ships and attacking American shipping. Jefferson rejected war and instead used economic threats and embargoes that ultimately hurt the U.S. more than Britain. The disputes with Britain continued after Jefferson left office, eventually leading to the War of 1812.

Despite the economic and political troubles caused by naval tensions with Britain, Jefferson was succeeded by his preferred successor in the form of James Madison. His presidency remained highly influential until the American Civil War, but his legacy has shifted and changed overtime, especially regarding his views on slavery. Nonetheless, historical rankings consistently place Jefferson among the nation's most esteemed presidents, and he has been extensively memorialized as an icon of American culture and American republicanism.