Jefferson as a president had an extreme anti-federalist viewpoint on government. He believed that states should hold more power. He also thought that property was a very important right for people to have. Jefferson expanded the right to vote to all white men, regardless of property ownership.
Jefferson followed the wording of the Constitution very tightly and did not approve of the "implied powers" idea. He thought it was either in the constitution or not at all. Despite his disregard for implied powers, he made the Louisiana Purchase himself.
The most substantial action Jefferson made during his presidency was the Louisiana purchase. Through this territorial acquisition, Jefferson doubled the size of the country. This purchase was able to happen because Napoleon of France was at war with the rest of Europe and saw little to gain from his land in America, so he sold it to help him in the war. The action helped America, but contradicted his beliefs of no implied powers.
Jefferson strongly opposed the Alien and Sedition acts made by John Adams. Jefferson and James Madison wrote the Kentucky and Virginia Resolutions in 1798. The Resolutions gave states the individual power to nullify any law made by the Federal Government if the state didn't approve of it.
During Jefferson's administration, he passed the Embargo Act of 1807. This Act banned exports out of the United States. This hurt America's economy and ended up being repealed in 1809.
During Jefferson's presidency, a war broke out between the US and Tripoli, which is a Mediterranean coastal city in Libya. The Pasha of Tripoli wanted money from the US for using waters near the city. The Tripolitan war ended in 1805 after peace was made.