After taking office in 1801, President Thomas Jefferson promised to shrink the government, including executive powers. But many of his domestic achievements received criticism for doing just the opposite. He resumed the capitol building project and designed additions to the White House. The 1803 Louisiana Purchase angered people both inside and out of his own political party. Many believed the president didn't have the constitutional authority to make such a decision on his own. The same year, the Lewis and Clark Expedition returned from exploring the new Louisiana Territory and helped spur westward migration. Shortly before their return, the Pike Expedition was dispatched to explore the southern border of the territory and gathered valuable military intelligence about the state of the Spanish empire in North America. President Jefferson signed into law a bill that banned the importation of slaves into the U.S. beginning in 1808.