On December 18, 1860, after Abraham Lincoln’s election and as Southern states threatened secession, Kentucky Senator John J. Crittenden, a Constitutional Unionist and political heir to Henry Clay, introduced a package of six constitutional amendments and four congressional resolutions. The central amendment revived the Missouri Compromise line at 36 degrees 30 minutes and extended it to the Pacific, banning slavery north of it and recognizing and protecting it south of it in all territory held or hereafter acquired. Because the Dred Scott decision of 1857 had already struck down the old line, the plan aimed to place it beyond the reach of the Supreme Court and future Congresses.

Other amendments barred Congress from abolishing slavery on federal property in slave states, interfering with the interstate slave trade, or ending slavery in Washington, D.C., unless Maryland and Virginia abolished it first, district residents consented, and owners were compensated. A final amendment declared that no future amendment could change these provisions. The resolutions targeted Northern personal liberty laws, while the North was offered only minor changes to the Fugitive Slave Act. From Springfield, Lincoln told Republicans to accept no compromise on the extension of slavery, warning of a covenant of war reaching to Tierra del Fuego. The plan failed in committee and in both houses, and the Peace Conference of February 1861, led by John Tyler, also collapsed.

• Under the plan, the federal government would compensate owners when crowds rescued fugitives, then sue the county where the rescue happened.
• The North’s concessions included ending the $10 versus $5 fee gap for commissioners and limiting marshals’ power to draft bystanders.
• Lincoln’s fear of expansion reflected 1850s filibuster expeditions such as William Walker’s seizure of Nicaragua, where he legalized slavery.
• When House Republicans offered to admit New Mexico immediately as a state, pro-slavery delegates rejected it.
• Ben Winters’ 2016 novel Underground Airlines imagines a present-day America in which the Crittenden Compromise passed.