Actually there were threats of secession (from both northern and southern states) prior to Lincoln's presidency. There IS Constitutional guidance. It's called the 10th amendment. There was , and is NO federal power to keep states from leaving the union. In fact, 3 states, when ratifying the Constitution included their right to secede.  He conceded to continued racism in Washington DC, Maryland, Delaware, Kentucky, Missouri, West Virginia. In fact, his IRS TAXED slave sales in those states! (Sales were illegal in DC, but slavery wasn't).  Perhaps instead of "liberal", I should have said, "left wing", "democrat" or "socialist."  Since the "People" of the individual "states" created the federal government, and they remained "people" of the individual states FIRST, then as citizens of the United "States", and not the other way around, Secession was legal & Constitutional. Lincoln applauded Texas secession from Mexico.  As did Colonists when they "seceded" from Great Britain.