Keeping the Union was not that important to Lincoln's critics. Today the President's critics want to hand over our Union's sovereignty to internationalists ostensibly to fight the WOT. Keeping the Union is not that important to them either.
That's why I say this war within a war is about whose America survives the WOT. It is worth blood (mostly theirs) to keep our Union.
1) The Dem Party was created for one purpose only---to protect slavery by keeping it out of the national debate, and, to accomplish that, the party had to "reward" loyalists with jobs, first party jobs, then government jobs. It was the most blatant kind of vote-buying, but its goal was to purchase loyalty so that no one would entertain anti-slave votes.
2) The GOP, despite "big government" policies like tariffs and RR subsidies, nevertheless had as its FIRST priority stopping slavery in the territories. As everyone knew---certainly Lincoln and Douglas---this essentially was "it" for slavery. It either was recognized as moral and legal, or it wasn't, and "what's good enough for Oklahoma was good enough for Ohio" would have been the next constitutional push. Thus, the Republicans were founded on a PRINCIPLE, while the Dems were founded on the ACQUISITION OF POWER. Now, there are terrible Republicans, and some pretty good Dems (like Zell Miller), but the parties have historical, and fundamental differences of their reasons for existence. The Dems still believe in slavery.