Appealing to the People was only constitutional when done through the amendment process. Madison told you that the Union was once and for all.
What do you call an election?
As for the People leaving the Union, that's where your education in the sovereignty pecking order begins.
The People don't have to follow the Constitution all the time. They can unmake it if they want to -- all they have to do is call a convention.
That's what the Southern Peoples did, when they withdrew from the Union.
The People make and unmake compacts and constitutions like you and I make our beds. Their actions are sovereign and above the Constitution. If they were not, arguendo, then how would they have the power to amend?
The People own the Constitution and are its Master -- not the other way around.
Lincoln just said what he did, to put something, anything, above the People so he could champion it (whatever it was) against the People's cause and justify himself in opposing the People in arms and in making himself the People's master by force of arms. He couldn't do it in his own name, so he had to have some excuse for calling out the Army to crush the People, which he did.
That's the dictionary definition of tyranny, by the way.