Abolition was clearly in the Republican platform but he was chosen as a moderate candidate in the convention vs some more firebrand candidates, in the hope that he would forestall war. This is not controversial -- you can read accounts of the convention in old newspapers.
The famous quote from Lincoln shows where his priorities lay: "If I could save the Union without freeing any slave, I would do it, and if I could save it by freeing all the slaves, I would do it, and if I could save it by freeing some and leaving others alone, I would also do that." https://www.nytimes.com/1862/08/24/archives/a-letter-from-pr...