Abraham Lincoln’s Cooper Union Address (February 27, 1860) was his most extended analysis of the Founding Fathers’ views on expanding slavery into America’s territories. Lincoln concluded that a majority of the signers of the Constitution thought it was constitutional for the federal government to regulate the process. (Northern Democrats thought the decision should be left to local option, or popular sovereignty. Southern Democrats, and SCOTUS, thought slave-owners should be able to take their slaves into any territory, no matter what the locals or Congress thought.)
I’ve found two mistakes Lincoln made (one of them involving a bogus letter by George Washington), which as far as I can tell have not been noticed since 1860. Down, rebs! They don’t weaken Lincoln’s argument, though they do show how onerous it was researching historical questions in those days.
I tell the story in the current issue of For the People, the newsletter of the Abraham Lincoln Association. You have to be a member to get a copy, or you can wait until January, when the ALA posts the past year’s newsletters on its website.
More on the Washington letter at my website.