Also, I forgot to mention that Lincoln urged all his Republicans to vote for the Corwin Amendment in March of 1861, and he wrote letters to all the state's governors urging them to pass this amendment. Both the House and Senate voted by a 2/3rds margin to approve the Corwin Amendment. 5 Northern states ratified it.
The Amendment guaranteed legal slavery indefinitely.
The 1860 Republicans were not against slavery, they were against losing all the money they were making from it.
Abraham Lincoln stated that he would endorse the Corwin amendment as a way of saving the Union, by preventing the southern state who had not already let the Union from leaving.
His thoughts at the time:
In a famous 1862 letter to Horace Greeley, Lincoln explained the reasons for his action and his long-held feelings on enslavement and equality:
“My paramount object in this struggle is to save the Union, and is not either to save or to destroy slavery. 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. What I do about slavery, and the colored race, I do because I believe it helps to save the Union; and what I forbear, I forbear because I do not believe it would help to save the Union. I shall do less whenever I shall believe what I am doing hurts the cause, and I shall do more whenever I shall believe doing more will help the cause. I shall try to correct errors when shown to be errors; and I shall adopt new views so fast as they shall appear to be true views.
“I have here stated my purpose according to my view of official duty; and I intend no modification of my oft-expressed personal wish that all men everywhere could be free.”
Source:
https://www.thoughtco.com/corwin-amendment-slavery-and-lincoln-4160928