Just to add to the other comments, actually Lincoln's view was that without the approval of Congress, his power on emancipation as President only applied to those areas that were currently in rebellion against the union.  So he acted as far as he thought the laws would allow it, in terms of eliminating slavery in 1863.  That's a far cry from using the issue as a pawn.

Neither Maryland (which had men enlisted on both sides), nor Delaware, nor New Jersey for that matter were in rebellion against the union.  Missouri and Kentucky likewise got a pass (despite local irregular action), as did Tennessee (under a recently re-established union government) and the parts of Virginia that became West Virginia.