In the early part of his term, Crittenden was concerned with quelling the violence in Kansas Territory. An opponent of the Kansas–Nebraska Act of 1854, Crittenden also opposed repealing the Missouri Compromise unless the North agreed to substitute popular sovereignty for the exclusion of slavery north of the 36°30' line. In early 1856, he proposed sending General Winfield Scott to the Kansas Territory to ensure that fair elections were held there, but the proposal was blocked by the Pierce administration. He did not agree with all of the act proposed by Robert Toombs to allow for a constitutional convention in Kansas Territory, but he supported it as a step to bring peace there. He regarded the ratifications of both the Topeka Constitution and the Lecompton Constitution as invalid, and made one of the most highly regarded speeches of his career in opposition to the latter. His substitute bill that would have resubmitted the Lecompton Constitution to Kansas for another ratification vote was supported by Republicans, but it was ultimately defeated. So great was Crittenden's influence after his actions on the Kansas question that Abraham Lincoln felt that Crittenden's endorsement of Stephen Douglas cost Lincoln the Illinois senatorial election in 1858.