Congressional Democrats--The Democratic Party dominated the South and the border states. They were generally in support of the slave system and the right of states to control their own economic system.
The Emancipation Proclamation freed only slaves in the Confederate States where the North had no authority at the time. However, it sets the stage for the 13th amendment (outlawing slavery) and would require Southern states to give up slavery to return to the Union. Northern Democrats believed this would encourage more war and remove all possibility for negotiation. This also created a mission for the war--end slavery. For many in the North this was not their motive.