Johnson's term in the House expired March 3, 1819, but by August, he had returned to the state legislature where he helped secure passage of a law that abolished imprisonment for debtors in Kentucky. In December 1819, he resigned his post in the state legislature to fill the Senate seat vacated by the resignation of John J. Crittenden. He was re-elected to a full term in 1822, so that in total, his Senate tenure ran from December 10, 1819 to March 4, 1829. In 1821, he introduced legislation chartering Columbian College (later The George Washington University) in Washington, D.C. During this time period, his views on Western expansion were clear. He believed that the US "empire of liberty" should extend across the continent, arguing in debates leading up to the Missouri Compromise that western expansion and emancipation should go hand in hand, acknowledging issues with white racism but advocating for gradual emancipation. Furthermore, he went against the ideas put forward by sympathizers of the Colonization movement, arguing in "favor of meaningfully incorporating people of color into a multiracial empire."