“The Constitution would not have been ratified if James Madison, who was unequaled in among delegates for scholarship of political organizations, had not with others supported positions that states retained sufficient sovereignty to secede as the last resort to a political impasse created by perceived usurpations or abuses of the federal government. This point was further emphasized by the fact the perpetual relationship language binding the colonies and colonists in the Articles of Confederation did not carry over into the Constitution.”
James Madison, Secession, & State Sovereignty
https://groups.google.com/forum/#!topic/alt.war.civil.usa/p5V_C8Hm8yw
+1.
Although 30 years later, Madison was against secession.